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.gcc gcc-4.4.0/gcc/config.gcc

--- gcc-4.4.0.orig/gcc/config.gcc	2009-04-17 13:58:41.000000000 +0200

+++ gcc-4.4.0/gcc/config.gcc	2009-05-27 21:38:31.000000000 +0200

@@ -2121,7 +2121,7 @@

 	if test x${sh_multilibs} = x ; then

 		case ${target} in

 		sh64-superh-linux* | \

-		sh[1234]*)	sh_multilibs=${sh_cpu_target} ;;

+		sh[1234]*)	sh_multilibs=`cd ${srcdir}/config/sh ; echo t-mlib-sh[1-4]* | sed 's:t-mlib-sh:,m:g;s: ::g'` ;;

 		sh64* | sh5*)	sh_multilibs=m5-32media,m5-32media-nofpu,m5-compact,m5-compact-nofpu,m5-64media,m5-64media-nofpu ;;

 		sh-superh-*)	sh_multilibs=m4,m4-single,m4-single-only,m4-nofpu ;;

 		sh*-*-linux*)	sh_multilibs=m1,m3e,m4 ;;