Merging r205144:

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r205144 | hfinkel | 2014-03-30 09:00:06 -0400 (Sun, 30 Mar 2014) | 7 lines

[PowerPC] Make -pg generate calls to _mcount not mcount

At least on REL6 (Linux/glibc 2.12), the proper symbol for generating gprof
data is _mcount, not mcount. Prior to this change, compiling with -pg would
generate linking errors (because of unresolved references to mcount), after
this change -pg seems at least minimally functional.

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llvm-svn: 206058