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)

Enable building a pure soft-float compiler without the need for a software

floating point library.

diff -dur gcc-4.0.4.orig/gcc/config.gcc gcc-4.0.4/gcc/config.gcc

--- gcc-4.0.4.orig/gcc/config.gcc	2007-02-02 19:12:28.000000000 +0100

+++ gcc-4.0.4/gcc/config.gcc	2007-02-02 19:12:07.000000000 +0100

@@ -677,7 +677,7 @@

 		tm_defines="TARGET_BIG_ENDIAN_DEFAULT=1 $tm_defines"

 		;;

 	esac

-	tmake_file="${tmake_file} arm/t-arm arm/t-linux"

+	tmake_file="${tmake_file} arm/t-arm arm/t-linux arm/t-arm-elf"

 	extra_parts="crtbegin.o crtbeginS.o crtend.o crtendS.o"

 	gnu_ld=yes

 	;;