[builtins] Deduplicate eqsf2 and gtsf2 via macro
The only difference between eqsf2 and gtsf2 is whether they return
1 or -1 on NaN. Rather than duplicating all the code, use a macro to
define the function twice and use an argument to decide whether to
negate the return value.
Differential Revision: https://reviews.llvm.org/D61919