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-4.2.3.orig/gcc/config/arm/linux-eabi.h gcc-4.2.3/gcc/config/arm/linux-eabi.h

--- gcc-4.2.3.orig/gcc/config/arm/linux-eabi.h	2007-09-01 17:28:30.000000000 +0200

+++ gcc-4.2.3/gcc/config/arm/linux-eabi.h	2008-05-25 23:47:36.000000000 +0200

@@ -47,7 +47,8 @@

 #define SUBTARGET_CPU_DEFAULT TARGET_CPU_arm10tdmi

 #undef SUBTARGET_EXTRA_LINK_SPEC

-#define SUBTARGET_EXTRA_LINK_SPEC " -m armelf_linux_eabi"

+#define SUBTARGET_EXTRA_LINK_SPEC	\

+	" %{mlittle-endian:-m armelf_linux_eabi} %{mbig-endian:-m armelfb_linux_eabi}"

 /* Use ld-linux.so.3 so that it will be possible to run "classic"

    GNU/Linux binaries on an EABI system.  */