https://bugs.gentoo.org/522586

delete the -I$includedir paths that get added to CPPFLAGS.  these are never
needed when building natively or cross-compiling and really get in the way
in both cases (upgrades/cross-compiling/etc...).

extracted from the upstream change:
http://ncurses.scripts.mit.edu/?p=ncurses.git;a=commitdiff;h=9ee3995474454b7d956885e0fe5c8cac2ae25d42#patch5

--- a/configure
+++ b/configure
@@ -18596,33 +18596,11 @@ CPPFLAGS="$CPPFLAGS -I. -I../include"
 if test "$srcdir" != "."; then
 	CPPFLAGS="$CPPFLAGS -I\${srcdir}/../include"
 fi
-if test "$GCC" != yes; then
-	CPPFLAGS="$CPPFLAGS -I\${includedir}"
-elif test "$includedir" != "/usr/include"; then
-	if test "$includedir" = '${prefix}/include' ; then
-		if test $prefix != /usr ; then
-			CPPFLAGS="$CPPFLAGS -I\${includedir}"
-		fi
-	else
-		CPPFLAGS="$CPPFLAGS -I\${includedir}"
-	fi
-fi
 
 ACPPFLAGS="-I. -I../include -I../../include $ACPPFLAGS"
 if test "$srcdir" != "."; then
 	ACPPFLAGS="-I\${srcdir}/../../include $ACPPFLAGS"
 fi
-if test "$GCC" != yes; then
-	ACPPFLAGS="$ACPPFLAGS -I\${includedir}"
-elif test "$includedir" != "/usr/include"; then
-	if test "$includedir" = '${prefix}/include' ; then
-		if test $prefix != /usr ; then
-			ACPPFLAGS="$ACPPFLAGS -I\${includedir}"
-		fi
-	else
-		ACPPFLAGS="$ACPPFLAGS -I\${includedir}"
-	fi
-fi
 
 ### Build up pieces for makefile rules
 echo "$as_me:18628: checking default library suffix" >&5