tcmode: Add -msgxx-glibc option if supported by the tools.

Basing this check off "arch == x86" is not strictly correct.
This option should be used on any toolchain where it is a valid
option to ensure that the build host libraries are ignored.

Signed-off-by: Drew Moseley <drew_moseley@mentor.com>
Merge pull request #40 from drewmoseley/fix-system-compiler-check

tcmode: Add -msgxx-glibc option if supported by the tools.