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)

diff -durN ltrace-0.4.orig/Makefile.in ltrace-0.4/Makefile.in

--- ltrace-0.4.orig/Makefile.in	2008-10-26 15:34:21.000000000 +0100

+++ ltrace-0.4/Makefile.in	2008-10-26 15:37:40.000000000 +0100

@@ -5,6 +5,7 @@

 OS		:= @HOST_OS@

 ARCH		:= $(shell echo "@HOST_ARCH@" |sed -e s/i.86/i386/      \

 						   -e s/sun4u/sparc64/  \

+						   -e s/alpha.*/alpha/  \

 						   -e s/arm.*/arm/      \

 						   -e s/sa110/arm/      \

 						   -e s/ppc64/ppc/      \