[PowerPC] Fix PR17354: Generate nop after local calls for PIC code.

When generating code for shared libraries, even local calls may be
intercepted, so we need a nop after the call for the linker to fix up the
TOC.  Test case adapted from the one provided in PR17354.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191440 91177308-0d34-0410-b5e6-96231b3b80d8