Add tests for default value of Tag_ABI_FP_rounding.

Change-Id: I051866d073fc6ce87ce3e693a3762da6d81f4393

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223217 91177308-0d34-0410-b5e6-96231b3b80d8
Emit ABI_FP_rounding attribute.

LLVM understands a -enable-sign-dependent-rounding-fp-math codegen option. When
the user has specified this option, the Tag_ABI_FP_rounding attribute should be
emitted with value 1. This option currently does not appear to disable
transformations and optimizations that assume default floating point rounding
behavior, AFAICT, but the intention should be recorded in the build attributes,
regardless of what the compiler actually does with the intention.

Change-Id: If838578df3dc652b6f2796b8d152545674bcb30e

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223218 91177308-0d34-0410-b5e6-96231b3b80d8