Silence warnings in libunwind.

* Remove the embedded directive undefined behavior by moving the
  the #ifdef out of the macro arguments.  [-Wembedded-directive]

* Remove the local variable shadowing warning by renaming
  frameInfo in UnwindLevel1-gcc-ext.c.  [-Wshadow]

* Explicitly cast the function pointer to void pointer to avoid
  the comparison between function pointer and void pointer.
  [-Wpedantic]

llvm-svn: 224690