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)

--- libc/nptl/sysdeps/unix/sysv/linux/alpha/sysdep-cancel.h    2006/10/29 21:48:06     1.6

+++ libc/nptl/sysdeps/unix/sysv/linux/alpha/sysdep-cancel.h    2007/03/13 21:28:03     1.7

@@ -55,6 +55,7 @@

 	bne	a3, SYSCALL_ERROR_LABEL;			\

 __LABEL($pseudo_ret)						\

 	.subsection 2;						\

+	cfi_startproc;						\

 __LABEL($pseudo_cancel)						\

 	subq	sp, 64, sp;					\

 	cfi_def_cfa_offset(64);					\

@@ -90,12 +91,13 @@

 	cfi_def_cfa_offset(0);					\

 __LABEL($syscall_error)						\

 	SYSCALL_ERROR_HANDLER;					\

+	cfi_endproc;						\

 	.previous

 # undef PSEUDO_END

 # define PSEUDO_END(sym)					\

-	.subsection 2;						\

 	cfi_endproc;						\

+	.subsection 2;						\

 	.size sym, .-sym

 # define SAVE_ARGS_0	/* Nothing.  */