Partial revert of r185568.

r186899 and r187061 added a preferred way for some architectures not to get
intrinsic generation for math builtins. So the code changes in r185568 can
now be undone (the test remains).



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@187079 91177308-0d34-0410-b5e6-96231b3b80d8