Disable x86 tail call optimizations that jump through GOT

For x86 targets, do not do sibling call optimization when materializing
the callee's address would require a GOT relocation. We can still do
tail calls to internal functions, hidden functions, and protected
functions, because they do not require this kind of relocation. It is
still possible to get GOT relocations when the user explicitly asks for
it with musttail or -tailcallopt, both of which are supposed to
guarantee TCO.

Based on a patch by Chih-hung Hsieh.

Reviewers: srhines, timmurray, danalbert, enh, void, nadav, rnk

Subscribers: joerg, davidxl, llvm-commits

Differential Revision: http://reviews.llvm.org/D9799

llvm-svn: 238487