cc/gcc: Apply CT_CC_GCC_DISABLE_PCH to do_cc_core.
Otherwise, users have to input --disable-libstdcxx-pch option
when building bare-metal CANADIAN C++ compiler.
Reviewed-by: Michael Hope
Signed-off-by: Zhenqiang Chen <zhenqiang.chen@linaro.org>
(transplanted from e3e1c9d45bddfbfb433ee9d583faf42fa31f50c0)
1 reporter_name="Alexander BIGGA"
2 reporter_url="http://sourceware.org/ml/crossgcc/2008-07/msg00000.html"