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 --git a/mpz/remove.c b/mpz/remove.c

--- a/mpz/remove.c

+++ b/mpz/remove.c

@@ -23,7 +23,7 @@

 unsigned long int

 mpz_remove (mpz_ptr dest, mpz_srcptr src, mpz_srcptr f)

 {

-  mpz_t fpow[40];		/* inexhaustible...until year 2020 or so */

+  mpz_t fpow[GMP_LIMB_BITS];		/* Really MP_SIZE_T_BITS */

   mpz_t x, rem;

   unsigned long int pwr;

   int p;

@@ -69,7 +69,7 @@

       mpz_set (dest, x);

     }

-  pwr = (1 << p) - 1;

+  pwr = (1L << p) - 1;

   mpz_clear (fpow[p]);

diff --git a/mpz/remove.c b/mpz/remove.c

--- a/mpz/remove.c

+++ b/mpz/remove.c

@@ -80,7 +80,7 @@

       mpz_tdiv_qr (x, rem, dest, fpow[p]);

       if (SIZ (rem) == 0)

 	{

-	  pwr += 1 << p;

+	  pwr += 1L << p;

 	  mpz_set (dest, x);

 	}

       mpz_clear (fpow[p]);