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>

22 May 2010 - Titus von Boxberg

Prerequisites and instructions for using ct-ng for building a cross toolchain on FreeBSD as host.

0) Tested on FreeBSD 8.0

1) Install (at least) the following ports

   archivers/lzma

   textproc/gsed

   devel/gmake

   devel/patch

   shells/bash

   devel/bison

   lang/gawk

   devel/automake110

   ftp/wget

   Of course, you should have /usr/local/bin in your PATH.

2) run ct-ng's configure with the following tool configuration:

   ./configure --with-sed=/usr/local/bin/gsed --with-make=/usr/local/bin/gmake \

   --with-patch=/usr/local/bin/gpatch

   [...other configure parameters as you like...]

3) proceed as described in general documentation

   but use gmake instead of make