syntax for loopbound pragma
generate loopbound attributes from pragma

* following the procedure as for loop hints in latest clang revisions
  (starting with 30974231cab08ddc43e78dfe224009f8555d0ec3)
loopbound metadata attached to loop cond branches
loopbounds: emit as llvm intrinsic
Merge branch 'master' into loopbound

Conflicts:
	include/clang/Basic/TokenKinds.def
	lib/Parse/ParsePragma.cpp
	lib/Parse/ParsePragma.h
	lib/Parse/ParseStmt.cpp
Merge branch 'loopbound'