http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54725
--- Comment #6 from Mike Frysinger <vapier at gentoo dot org> 2012-09-28 23:12:08 UTC --- (In reply to comment #5) that's half the equation. the other half is the build system support. in gcc/Makefile.in, they do: CFLAGS-c-family/c-opts.o += @TARGET_SYSTEM_ROOT_DEFINE@ but you can't do that in gcc/fortran/Make-lang.in. you can't use $(TARGET_SYSTEM_ROOT_DEFINE) either because the variable is only AC_SUBST(). so you could add this line to gcc/Makefile.in: CFLAGS-fortran/cpp.o += @TARGET_SYSTEM_ROOT_DEFINE@ and it'd work. this seems to be how they propagate the define into the CFLAGS-c-family/c-opts.o variable, so maybe this is OK. alternatively, gcc/Makefile.in does setup $(COMPILER_DEFINES), so adding this to gcc/fortran/Make-lang.in works: CFLAGS-fortran/cpp.o += $(DRIVER_DEFINES) but i'm sure that's the wrong answer. the other alternative is to declare a "static const char *sysroot" inside of gcc/fortran/gfortranspec.c and then initialize gfc_cpp_option.sysroot via that. this works because gfortranspec.c is compiled already with $(COMPILER_DEFINES). i'm wait out of my depth, so i don't know what the "right" answer is :).
