Support IRgen of sqrt -> llvm.sqrt, pow -> llvm.pow.

 - Define pow[lf]?, sqrt[lf]? as builtins.

 - Add -fmath-errno option which binds to LangOptions.MathErrno

 - Add new builtin flag Builtin::Context::isConstWithoutErrno for
   functions which can be marked as const if errno isn't respected for
   math functions. Sema automatically marks these functions as const
   when they are defined, if MathErrno=0.

 - IRgen uses const attribute on sqrt and pow library functions to
   decide if it can use the llvm intrinsic.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@64689 91177308-0d34-0410-b5e6-96231b3b80d8
9 files changed