Add the i128 builtin type to LLVM.

The i128 type is needed as a builtin type in order to support the v1i128 vector
type. The PowerPC ABI requires that the i128 and v1i128 types are handled
differently when passed as parameters to functions (i128 is passed in pairs of
GPRs, v1i128 is passed in a single vector register). 

http://reviews.llvm.org/D8564

llvm-svn: 235196