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)

This patch is courtesy of OpenEmbedded, by Khem Raj <raj.khem@gmail.com>

http://cgit.openembedded.org/cgit.cgi/openembedded/commit/?id=b85b779688f0abc389e3c25d06b54de8b86385c1

Index: ltrace-0.5.3/Makefile.in

===================================================================

--- ltrace-0.5.3.orig/Makefile.in	2009-10-23 22:06:08.130304691 -0700

+++ ltrace-0.5.3/Makefile.in	2009-10-23 22:06:53.160369614 -0700

@@ -39,6 +39,8 @@ ltrace:		main.o libltrace.a

 libltrace.a: 	sysdeps/sysdep.o $(OBJ)

 		$(AR) rcv $@ $^

+$(OBJ):		sysdeps/sysdep.o

+

 sysdeps/sysdep.o: dummy

 		$(MAKE) -C sysdeps/$(OS)