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:

 bits/sysnum.h needs a cross compiler to be built. Fortunately, this

 header is not needed to build gcc. Move generation of this header.

 Index: uClibc/Makefile.in

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

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

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

 @@ -91,6 +91,11 @@

  			$(LN) -fs $$i .; \

  		done; \

  	fi

 +ifeq ($(UCLIBC_HAS_LOCALE),y)

 +	$(MAKE) locale_headers

 +endif

 +

 +pregen: headers

  	$(Q)\

  	set -e; \

  	cd $(top_builddir); \

 @@ -102,12 +107,7 @@

  	else \

  		mv -f $$tmp include/bits/sysnum.h; \

  	fi

 -ifeq ($(UCLIBC_HAS_LOCALE),y)

 -	$(MAKE) locale_headers

 -endif

 -pregen: headers

 -

  install: install_runtime install_dev