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)

--- glibc-2.5/sysdeps/unix/sysv/linux/alpha/sigsuspend.S.orig	2006-10-22 22:17:01.000000000 +0200

+++ glibc-2.5/sysdeps/unix/sysv/linux/alpha/sigsuspend.S	2006-10-22 22:18:05.000000000 +0200

@@ -31,3 +31,21 @@

 libc_hidden_def (__sigsuspend)

 weak_alias (__sigsuspend, sigsuspend)

 strong_alias (__sigsuspend, __libc_sigsuspend)

+

+#ifndef NO_CANCELLATION

+	.globl __sigsuspend_nocancel;

+	.align 4;

+	.type __sigsuspend_nocancel, @function;

+	.usepv __sigsuspend_nocancel, std;

+	cfi_startproc;

+__LABEL(__sigsuspend_nocancel)

+	ldgp    gp, 0(pv);

+	PSEUDO_PROF;

+	PSEUDO_PREPARE_ARGS

+	lda     v0, SYS_ify(sigsuspend);

+	call_pal PAL_callsys;

+	bne     a3, SYSCALL_ERROR_LABEL;

+	ret;

+	cfi_endproc;

+	.size __sigsuspend_nocancel, .-__sigsuspend_nocancel

+#endif