Options included in CC/CXX vs. in gb_CFLAGS/gb_CXXFLAGS

I think there is some fuzziness about what compiler options should be
part of the CC/CXX variables and what should be in
gb_CFLAGS/gb_CXXFLAGS.

In some cases, like my Mac build tree that uses the 10.4 SDK, from
Xcode 3 installed in /Xcode3, gb_CXXFLAGS contains at least one flag
that apparently *must* be used for also external projects (well,
liborcus in particular) to compile successfully.  This is the
-isysroot from solenv/gbuild/platform/macosx.mk.

In different Mac build environments, this apparently is not the case,
there the gcc from Xcode 3 (or 2 even) works fine for liborcus even if
no -isysroot is used. These are perhaps older versions of the OS,
and/or with Xcode 3 in a different location?

In other cases ("normal" Linuxes?) gb_CXXFLAGS contains just optional
flags that will in fact hurt an external project that isn't prepared
for them, like -Werror.

Should the -isysroot flag actually be part ot CC/CXX, not gb_CXXFLAGS?
Should configure.in and macosx.mk be modified thusly?

--tml