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)

reporter_name="Nate CASE"

reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00016.html"

reporter_comment="This is a sample config file for Freescale e500v2 processors (e.g.,

MPC8548, MPC8572).  It uses eglibc (for e500/SPE patches) and a recent

gcc (4.3.1, for e500v2 DPFP support) and will generate appropriate

dual-precision floating point instructions by default.

Note: If building a Linux kernel with this toolchain, you will want to

make sure -mno-spe AND -mspe=no are passed to gcc to prevent SPE

ABI/instructions from getting into the kernel (which is currently

unsupported).  At this time, the kernel build system only passes

-mno-spe by default (this should be fixed soon hopefully)."