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 -dur strace-4.5.16.orig/syscall.c strace-4.5.16/syscall.c

 --- strace-4.5.16.orig/syscall.c	2007-07-14 19:21:44.000000000 +0200

 +++ strace-4.5.16/syscall.c	2007-07-14 19:22:49.000000000 +0200

 @@ -125,6 +125,18 @@

  #define TP TRACE_PROCESS

  #define TS TRACE_SIGNAL

 +#ifndef HAVE_STATFS64

 +/*

 + * Ugly hacks for systems that do not have LFS

 + */

 +

 +#define sys_truncate64  sys_truncate

 +#define sys_ftruncate64 sys_ftruncate

 +#define sys_getdents64  sys_getdents

 +#define sys_statfs64    sys_statfs

 +#define sys_fstatfs64   sys_fstatfs

 +#endif

 +

  static const struct sysent sysent0[] = {

  #include "syscallent.h"

  };