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 using a shell other than bash.

Courtesy "Martin Guy" <martinwguy@yahoo.it>

http://sourceware.org/ml/crossgcc/2008-08/msg00037.html

--- binutils-2.18.orig/ld/genscripts.sh	2007-08-12 20:00:07.000000000 +0100

+++ binutils-2.18/ld/genscripts.sh	2008-08-25 16:09:54.000000000 +0100

@@ -398,9 +398,11 @@

     . $em_script

     em_script=$current_script

   }

-  fragment()

+  

+  alias fragment='em_lineno=$LINENO; fragment_em'

+  fragment_em()

   {

-    local lineno=$[${BASH_LINENO[0]} + 1]

+    local lineno=$[$em_lineno + 1]

     echo >> e${EMULATION_NAME}.c "#line $lineno \"$em_script\""

     cat >> e${EMULATION_NAME}.c

   }