gcc-configure-common.inc: Stop gcc looking at build system paths

There were puzzling failures when you make a force recompile of any gcc
component. The error was in do_configure with cross-compilation badness
being detected in config.log files.

gcc is different in that many of the config.log files are generated during
the do_compile phase. This means this host contamination issue has always
been present but only shows up on a rebuild.

The fix is to force the appropriate configuration variable to "none required"
then gcc won't look in the bad locations.

[YOCTO #2279]

(From OE-Core rev: e7135f14f3ef37f93f5c28b319464f3d6dd9b8da)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/gcc/gcc-configure-common.inc

@@ -107,6 +107,10 @@ do_configure () {
 	export CXXFLAGS_FOR_BUILD="${BUILD_CXXFLAGS}"
 	export LDFLAGS_FOR_BUILD="${BUILD_LDFLAGS}"
 	export ARCH_FLAGS_FOR_TARGET="${ARCH_FLAGS_FOR_TARGET}"
+	# We need to set this else there is cross-compilation badness
+	# in the config.log files (which might not get generated until do_compile
+	# hence being missed by the insane do_configure check).
+	export gcc_cv_collect2_libs="none required"
 	(cd ${S} && gnu-configize) || die "failure running gnu-configize"
 
 	oe_runconf