scripts: remove . from $PATH

Add CT_SanitizePath function which removes entries referring to ., /tmp
and non-existing directories from $PATH, and call it early in the
build script.

If . is in PATH, gcc-4.4.4 build breaks:

[ALL ] checking what assembler to use...
/tmp/build/targets/arm-unknown-linux-uclibcgnueabi/build/gcc-core-static/arm-unknown-linux-uclibcgnueabi/bin/as
...
[ALL ] config.status: creating as

i.e. "as" is supposed to be the arm-unknown-linux-uclibcgnueabi cross assembler,
but config.status creates a local "as" script which is calling the
host assembler.

Signed-off-by: Johannes Stezenbach <js@sig21.net>
[Yann E. MORIN: style fixes + explanations]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 20dd8cef1c8adff0aa3e78ae6d7acfbc45ed5a83)

diff -durN gcc-4.4.0.orig/gcc/config/arm/linux-eabi.h gcc-4.4.0/gcc/config/arm/linux-eabi.h

--- gcc-4.4.0.orig/gcc/config/arm/linux-eabi.h	2007-11-08 14:44:09.000000000 +0100

+++ gcc-4.4.0/gcc/config/arm/linux-eabi.h	2009-05-27 21:38:26.000000000 +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.  */