PGO: Declare zero-argument C functions as foo(void)

It turns out this is C code.  Specify foo(void).

<rdar://problem/15943240>

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@204396 91177308-0d34-0410-b5e6-96231b3b80d8