Change setup.py to respect the SYSROOT environment variable

--- a/setup.py
+++ b/setup.py
@@ -455,10 +455,14 @@
 
     def detect_modules(self):
         global disable_ssl
+
+        # We must respect the user specified sysroot!
+        sysroot = os.getenv('SYSROOT', '')
+
         # Ensure that /usr/local is always used
         if not cross_compiling:
-            add_dir_to_list(self.compiler.library_dirs, '/usr/local/@@GENTOO_LIBDIR@@')
-            add_dir_to_list(self.compiler.include_dirs, '/usr/local/include')
+            add_dir_to_list(self.compiler.library_dirs, sysroot + '/usr/local/@@GENTOO_LIBDIR@@')
+            add_dir_to_list(self.compiler.include_dirs, sysroot + '/usr/local/include')
         if cross_compiling:
             self.add_gcc_paths()
         self.add_multiarch_paths()
@@ -504,9 +508,15 @@
             # building a framework with different architectures than
             # the one that is currently installed (issue #7473)
             add_dir_to_list(self.compiler.library_dirs,
-                            sysconfig.get_config_var("LIBDIR"))
+                            sysroot + sysconfig.get_config_var("LIBDIR"))
             add_dir_to_list(self.compiler.include_dirs,
-                            sysconfig.get_config_var("INCLUDEDIR"))
+                            sysroot + sysconfig.get_config_var("INCLUDEDIR"))
+
+        # We should always look into sysroot/usr/include and consider
+        # also the lib dirs there for searching for files
+        add_dir_to_list(self.compiler.include_dirs, sysroot + '/usr/include')
+        add_dir_to_list(self.compiler.library_dirs, sysroot + '/@@GENTOO_LIBDIR@@')
+        add_dir_to_list(self.compiler.library_dirs, sysroot + '/usr/@@GENTOO_LIBDIR@@')
 
         try:
             have_unicode = unicode
@@ -527,6 +537,9 @@
                 '/@@GENTOO_LIBDIR@@', '/usr/@@GENTOO_LIBDIR@@',
                 ):
                 add_dir_to_list(lib_dirs, d)
+        # Ignore previous settings.
+        lib_dirs = self.compiler.library_dirs
+        inc_dirs = self.compiler.include_dirs
         exts = []
         missing = []
 
@@ -778,11 +791,11 @@
             elif curses_library:
                 readline_libs.append(curses_library)
             elif self.compiler.find_library_file(lib_dirs +
-                                                     ['/usr/@@GENTOO_LIBDIR@@/termcap'],
+                                                     [sysroot + '/usr/@@GENTOO_LIBDIR@@/termcap'],
                                                      'termcap'):
                 readline_libs.append('termcap')
             exts.append( Extension('readline', ['readline.c'],
-                                   library_dirs=['/usr/@@GENTOO_LIBDIR@@/termcap'],
+                                   library_dirs=[sysroot + '/usr/@@GENTOO_LIBDIR@@/termcap'],
                                    extra_link_args=readline_extra_link_args,
                                    libraries=readline_libs) )
         else:
@@ -805,20 +818,20 @@
                                libraries=math_libs) )
         # Detect SSL support for the socket module (via _ssl)
         search_for_ssl_incs_in = [
-                              '/usr/local/ssl/include',
-                              '/usr/contrib/ssl/include/'
+                              sysroot + '/usr/local/ssl/include',
+                              sysroot + '/usr/contrib/ssl/include/'
                              ]
         ssl_incs = find_file('openssl/ssl.h', inc_dirs,
                              search_for_ssl_incs_in
                              )
         if ssl_incs is not None and not disable_ssl:
             krb5_h = find_file('krb5.h', inc_dirs,
-                               ['/usr/kerberos/include'])
+                               [sysroot + '/usr/kerberos/include'])
             if krb5_h:
                 ssl_incs += krb5_h
         ssl_libs = find_library_file(self.compiler, 'ssl',lib_dirs,
-                                     ['/usr/local/ssl/lib',
-                                      '/usr/contrib/ssl/lib/'
+                                     [sysroot + '/usr/local/ssl/lib',
+                                      sysroot + '/usr/contrib/ssl/lib/'
                                      ] )
 
         if (ssl_incs is not None and
@@ -968,6 +981,7 @@
             db_inc_paths.append('/usr/local/include/db3%d' % x)
             db_inc_paths.append('/pkg/db-3.%d/include' % x)
             db_inc_paths.append('/opt/db-3.%d/include' % x)
+        db_inc_paths = [sysroot + x for x in db_inc_paths]
 
         if cross_compiling:
             db_inc_paths = []
@@ -1121,6 +1135,7 @@
                            ]
         if cross_compiling:
             sqlite_inc_paths = []
+        sqlite_inc_paths = [sysroot + x for x in sqlite_inc_paths]
         MIN_SQLITE_VERSION_NUMBER = (3, 0, 8)
         MIN_SQLITE_VERSION = ".".join([str(x)
                                     for x in MIN_SQLITE_VERSION_NUMBER])
@@ -1222,7 +1237,7 @@
         # we do not build this one.  Otherwise this build will pick up
         # the more recent berkeleydb's db.h file first in the include path
         # when attempting to compile and it will fail.
-        f = "/usr/include/db.h"
+        f = sysroot + "/usr/include/db.h"
 
         if host_platform == 'darwin':
             if is_macosx_sdk_path(f):
@@ -1835,7 +1850,7 @@
         # For 8.4a2, the X11 headers are not included. Rather than include a
         # complicated search, this is a hard-coded path. It could bail out
         # if X11 libs are not found...
-        include_dirs.append('/usr/X11R6/include')
+        include_dirs.append(sysroot + '/usr/X11R6/include')
         frameworks = ['-framework', 'Tcl', '-framework', 'Tk']
 
         # All existing framework builds of Tcl/Tk don't support 64-bit
@@ -1879,6 +1894,9 @@
         if self.detect_tkinter_explicitly():
             return
 
+        # We must respect the user specified sysroot!
+        sysroot = os.getenv('SYSROOT', '')
+
         # Rather than complicate the code below, detecting and building
         # AquaTk is a separate method. Only one Tkinter will be built on
         # Darwin - either AquaTk, if it is found, or X11 based Tk.
@@ -1934,16 +1952,16 @@
         if host_platform == 'sunos5':
             include_dirs.append('/usr/openwin/include')
             added_lib_dirs.append('/usr/openwin/lib')
-        elif os.path.exists('/usr/X11R6/include'):
-            include_dirs.append('/usr/X11R6/include')
-            added_lib_dirs.append('/usr/X11R6/@@GENTOO_LIBDIR@@')
-        elif os.path.exists('/usr/X11R5/include'):
-            include_dirs.append('/usr/X11R5/include')
-            added_lib_dirs.append('/usr/X11R5/@@GENTOO_LIBDIR@@')
+        elif os.path.exists(sysroot + '/usr/X11R6/include'):
+            include_dirs.append(sysroot + '/usr/X11R6/include')
+            added_lib_dirs.append(sysroot + '/usr/X11R6/@@GENTOO_LIBDIR@@')
+        elif os.path.exists(sysroot + '/usr/X11R5/include'):
+            include_dirs.append(sysroot + '/usr/X11R5/include')
+            added_lib_dirs.append(sysroot + '/usr/X11R5/@@GENTOO_LIBDIR@@')
         else:
             # Assume default location for X11
-            include_dirs.append('/usr/X11/include')
-            added_lib_dirs.append('/usr/X11/@@GENTOO_LIBDIR@@')
+            include_dirs.append(sysroot + '/usr/X11/include')
+            added_lib_dirs.append(sysroot + '/usr/X11/@@GENTOO_LIBDIR@@')
 
         # If Cygwin, then verify that X is installed before proceeding
         if host_platform == 'cygwin':