[SystemZ] Specify required features for builtins.

BuiltinsSystemZ.def is extended to include the required processor
features per intrinsic.

New test test/CodeGen/builtins-systemz-error2.c that checks for
expected errors when instrinsics are used with a subtarget that does
not support the required feature (e.g. vector support).

Reviewed by Ulrich Weigand.

llvm-svn: 264873