[FPEnv][NFC] Change test to conform to strictfp attribute rules.
In particular, the function definition is not marked strictfp despite
containing a function marked strictfp. Also, if any function call is marked
strictfp then all function calls in that function must be marked.
This change to move the one strictfp call to a new properly marked function
meets all the new rules.
Tested with a stricter version of D68233.
Reviewed by: spatel
Approved by: spatel
Differential Revision: https://reviews.llvm.org/D68713