arch/mips: add experimental mips64 samples

Both toolchains were tested to successfully:
- _build_ busybox, giving respectively an n32 and an n64 binary
although it has not been run-tested.
- build linux-2.6.36-rc3 for Loongson, giving an n64 vmlinux
(which is expected, due to the way the kernel is built),
and the kernel properly boots!

Credits are due to Julien MOUTHINO (julm on freenode#uClibc) for
testing that the kernel boots on his hardware! Cheers! ;-)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

--- trunk/src/acos.c	2009/12/08 16:49:43	733

+++ trunk/src/acos.c	2009/12/09 20:51:38	734

@@ -188,10 +188,7 @@

   else

     rnd_im = rnd_im == GMP_RNDU ? GMP_RNDD

       : rnd_im == GMP_RNDD ? GMP_RNDU

-#if MPFR_VERSION_MAJOR >= 3

-      : rnd_im == GMP_RNDA ? GMP_RNDZ

-#endif

-      : rnd_im;

+      : rnd_im; /* both RNDZ and RNDA map to themselves for -asin(z) */

   rnd1 = RNDC(GMP_RNDN, rnd_im);

   mpfr_init2 (pi_over_2, p);

   for (;;)