[Bug target/56279] Unwanted directory is added to include search path when building for MingGW with --native-system-header-dir

[karlson2k at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56279

--- Comment #1 from Evgeny Grin <karlson2k at gmail dot com> 2013-02-10 23:04:16 UTC ---
This unwanted dir is added by blindly overriding directory in
gcc/config/i386/mingw32.h:

#undef NATIVE_SYSTEM_HEADER_DIR
#define NATIVE_SYSTEM_HEADER_DIR "/mingw/include"

as result of fixing bug 52947. I think, it needs more improvement. At least for
MinGW this directory should be relative to GCC files, as other include dirs.
And cppdefault.c should be corrected like this:

#ifdef NATIVE_SYSTEM_HEADER_DIR
    /* /usr/include comes dead last.  */
    { NATIVE_SYSTEM_HEADER_DIR, NATIVE_SYSTEM_HEADER_COMPONENT, 0, 0,
      NATIVE_SYSTEM_HEADER_DIR_ADD_SYSROOT, 0 },
#endif

similar to GPLUSPLUS_INCLUDE_DIR part in cppdefault.c.