[TLI] Fix NumParams==0 prototype checking typo.

There was a typo in r267758. It caused invalid accesses when
given something like "void @free(...)", as NumParams == 0, and
we then try to look at the 0th parameter.

Turns out, most of these were untested; add both attribute
and missing-prototype checks for all libc libfuncs.

Differential Revision: http://reviews.llvm.org/D20543

llvm-svn: 270750