Allow overriding the calculated GOBJECT_INTROSPECTION_LIBDIR path so that we
may specify a default search path for typelib files in situations where it is
inconvenient or impossible to set GI_TYPELIB_PATH through the environment.

diff --git a/meson.build b/meson.build
index e5205e3..acbc295 100644
--- a/meson.build
+++ b/meson.build
@@ -100,7 +100,7 @@ else
 endif
 girdir = join_paths(gir_dir_prefix, 'gir-1.0')
 config.set_quoted('GIR_DIR', girdir)
-config.set_quoted('GOBJECT_INTROSPECTION_LIBDIR', join_paths(get_option('prefix'), get_option('libdir')))
+config.set_quoted('GOBJECT_INTROSPECTION_LIBDIR', get_option('gi_libdir'))

 foreach type : ['char', 'short', 'int', 'long']
   size = cc.sizeof(type)
diff --git a/meson_options.txt b/meson_options.txt
index dff9be8..de8fb16 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -45,3 +45,7 @@ option('build_introspection_data', type: 'boolean', value : true,
 option('gi_cross_pkgconfig_sysroot_path', type: 'string',
   description: 'Specify a sysroot path to prepend to pkgconfig output (useful when cross-compiling)'
 )
+
+option('gi_libdir', type: 'string',
+  description: 'Specify a hardcoded value for GOBJECT_INTROSPECTION_LIBDIR.'
+)