Don't generate floating point stubs for mips16 code if the function

Don't generate floating point stubs for mips16 code if the function
is actually an instrinsic that will not occur in libc. This list here
is not exhaustive but fixes the one places in test-suite where this occurs.
I have filed a bug against myself to research the full list and add them
to the array of such cases. In the future, actual stub generation will occur
in a later phase and we won't need this code because we will know at that time
during the compilation that in fact no helper function was even needed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188149 91177308-0d34-0410-b5e6-96231b3b80d8