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)

YEM-20070519:

Patch from Bernhard Fischer <rep.dot.nop@gmail.com> on the uClibc mailing

list ( http://www.uclibc.org/lists/uclibc/2008-January/018940.html ) above

the 400-bits_sysnum_h.patch.

Index: uClibc/Makefile.in

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

--- uClibc/Makefile.in	(revision 18651)

+++ uClibc/Makefile.in	(working copy)

@@ -114,7 +116,7 @@ install: install_runtime install_dev

 RUNTIME_PREFIX_LIB_FROM_DEVEL_PREFIX_LIB=$(shell $(top_srcdir)extra/scripts/relative_path.sh $(DEVEL_PREFIX)lib $(RUNTIME_PREFIX)lib)

 # Installs header files.

-install_headers:

+install_headers: headers

 	$(INSTALL) -d $(PREFIX)$(DEVEL_PREFIX)include

 	printf ".svn\n.cvsignore\nCVS\n" > tar_exclude ; \

 	$(TAR) -chf - -X tar_exclude include \