[CodeGen] map sqrt libcalls to llvm.sqrt when errno is not set

[CodeGen] map sqrt libcalls to llvm.sqrt when errno is not set

The LLVM sqrt intrinsic definition changed with:
D28797
...so we don't have to use any relaxed FP settings other than errno handling.

This patch sidesteps a question raised in PR27435:
https://bugs.llvm.org/show_bug.cgi?id=27435

Is a programmer using __builtin_sqrt() invoking the compiler's intrinsic definition of sqrt or the mathlib definition of sqrt?

But we have an answer now: the builtin should match the behavior of the libm function including errno handling.

Differential Revision: https://reviews.llvm.org/D39204

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@317031 91177308-0d34-0410-b5e6-96231b3b80d8