[PGO] Unify section name, section symbol definitions (Linux)
[PGO] Unify section name, section symbol definitions (Linux)

 Replace hard-coded references to names to key section and section
 symbols with common macro definitions.





git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@253897 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt