[FPEnv] Strict FP tests should use the requisite function attributes.

A set of function attributes is required in any function that uses constrained
floating point intrinsics. None of our tests use these attributes.

This patch fixes this.

These tests have been tested against the IR verifier changes in D68233.

Reviewed by:	andrew.w.kaylor, cameron.mcinally, uweigand
Approved by:	andrew.w.kaylor
Differential Revision:	https://reviews.llvm.org/D67925

llvm-svn: 373761