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)

Original patch from gentoo: gentoo/src/patchsets/gcc/4.3.1/gentoo/51_all_gcc-3.4-libiberty-pic.patch

diff -durN gcc-4.3.1.orig/libiberty/Makefile.in gcc-4.3.1/libiberty/Makefile.in

--- gcc-4.3.1.orig/libiberty/Makefile.in	2007-07-25 08:26:45.000000000 +0200

+++ gcc-4.3.1/libiberty/Makefile.in	2008-06-10 14:58:02.000000000 +0200

@@ -225,6 +225,7 @@

 	  $(AR) $(AR_FLAGS) $(TARGETLIB) \

 	    $(REQUIRED_OFILES) $(EXTRA_OFILES) $(LIBOBJS); \

 	  $(RANLIB) $(TARGETLIB); \

+	  cp $(TARGETLIB) ../ ; \

 	  cd ..; \

 	else true; fi