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)

 --- gcc-4.3.4/libffi/src/arm/sysv.S	

 +++ gcc-4.3.4/libffi/src/arm/sysv.S	

 @@ -235,7 +235,7 @@ ARM_FUNC_START ffi_closure_SYSV

  	stmfd	sp!, {ip, lr}

  	UNWIND .save	{r0, lr}

  	add	r2, sp, #8

 -	.pad #16

 +	UNWIND .pad #16

  	sub	sp, sp, #16

  	str	sp, [sp, #8]

  	add	r1, sp, #8