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-4.3.2.orig/gcc/config/arm/linux-eabi.h	2009-09-08 23:46:44.000000000 +0200

+++ gcc-4.3.2/gcc/config/arm/linux-eabi.h	2009-09-08 23:46:51.000000000 +0200

@@ -44,7 +44,7 @@

    The ARM10TDMI core is the default for armv5t, so set

    SUBTARGET_CPU_DEFAULT to achieve this.  */

 #undef  SUBTARGET_CPU_DEFAULT

-#define SUBTARGET_CPU_DEFAULT TARGET_CPU_arm10tdmi

+#define SUBTARGET_CPU_DEFAULT TARGET_CPU_arm9tdmi

 /* TARGET_BIG_ENDIAN_DEFAULT is set in

    config.gcc for big endian configurations.  */