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]);