scripts, cc/gcc: do not fail on existing symlinks or build.log

If the user builds a toolchain over an existing one, so, without removing
CT_PREFIX_DIR, the build fails as the symlinks already exist, as does the
build.log.

This can also happen (for build.log) if the user first ran in download-
or extract-only.

Patch (with no SoB) originally from:
Phil Wilshire <phil.wilshire@overturenetworks.com>

Modified by me as it did not apply cleanly.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 1ebc2248cc60230cd53ff94ae8f8f1e3261461a3)

--- 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