Add missing builtins to altivec.h for ABI compliance (vol. 2)

This patch corresponds to review:
http://reviews.llvm.org/D10875

The bulk of the second round of additions to altivec.h.
The following interfaces were added:
vector double vec_floor(vector double)
vector double vec_madd(vector double, vector double, vector double)
vector float vec_msub(vector float, vector float, vector float)
vector double vec_msub(vector double, vector double, vector double)
vector float vec_mul(vector float, vector float)
vector double vec_mul(vector double, vector double)
vector float vec_nmadd(vector float, vector float, vector float)
vector double vec_nmadd(vector double, vector double, vector double)
vector double vec_nmsub(vector double, vector double, vector double)
vector double vec_nor(vector double, vector double)
vector double vec_or(vector double, vector double)
vector float vec_rint(vector float)
vector double vec_rint(vector double)
vector float vec_nearbyint(vector float)
vector double vec_nearbyint(vector double)
vector float vec_sqrt(vector float)
vector double vec_sqrt(vector double)
vector double vec_rsqrte(vector double)
vector double vec_sel(vector double, vector double, vector unsigned long long)
vector double vec_sel(vector double, vector double, vector unsigned long long)
vector double vec_sub(vector double, vector double)
vector double vec_trunc(vector double)
vector double vec_xor(vector double, vector double)
vector double vec_xor(vector double, vector bool long long)
vector double vec_xor(vector bool long long, vector double)

New VSX paths for the following interfaces:
vector float vec_madd(vector float, vector float, vector float)
vector float vec_nmsub(vector float, vector float, vector float)
vector float vec_rsqrte(vector float)
vector float vec_trunc(vector float)
vector float vec_floor(vector float)

llvm-svn: 241399