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)

diff -ur gcc-4.4.1-orig/libjava/Makefile.in gcc-4.4.1/libjava/Makefile.in

--- gcc-4.4.1-orig/libjava/Makefile.in	2009-08-04 04:12:27.000000000 -0700

+++ gcc-4.4.1/libjava/Makefile.in	2009-09-23 22:03:15.750951483 -0700

@@ -8874,6 +8874,9 @@

 ecjx$(EXEEXT): $(ecjx_OBJECTS) $(ecjx_DEPENDENCIES) 

 	@rm -f ecjx$(EXEEXT)

 	$(ecjx_LINK) $(ecjx_LDFLAGS) $(ecjx_OBJECTS) $(ecjx_LDADD) $(LIBS)

+ecjx.$(OBJEXT): $(ecjx_SOURCES)

+	@rm -f ecjx.$(OBJEXT)

+	$(CC_FOR_BUILD) $(BUILD_CFLAGS) -c -o $@ $<

 gappletviewer$(EXEEXT): $(gappletviewer_OBJECTS) $(gappletviewer_DEPENDENCIES) 

 	@rm -f gappletviewer$(EXEEXT)

 	$(gappletviewer_LINK) $(gappletviewer_LDFLAGS) $(gappletviewer_OBJECTS) $(gappletviewer_LDADD) $(LIBS)