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)

Original patch from: mpf_set_str.c.4.diff

-= BEGIN original header =-

-= END original header =-

diff -durN gmp-4.2.4.orig/mpf/set_str.c gmp-4.2.4/mpf/set_str.c

--- gmp-4.2.4.orig/mpf/set_str.c	2008-08-25 16:11:37.000000000 +0200

+++ gmp-4.2.4/mpf/set_str.c	2009-03-08 18:36:16.000000000 +0100

@@ -137,7 +137,12 @@

       c = (unsigned char) *++str;

     }

+  /* Default base to decimal.  */

+  if (base == 0)

+    base = 10;

+

   exp_base = base;

+

   if (base < 0)

     {

       exp_base = 10;

@@ -165,10 +170,6 @@

 	return -1;

     }

-  /* Default base to decimal.  */

-  if (base == 0)

-    base = 10;

-

   /* Locate exponent part of the input.  Look from the right of the string,

      since the exponent is usually a lot shorter than the mantissa.  */

   expptr = NULL;