Handle instrumentation of scalar single-precision (_ss) intrinsics

Instrumentation of scalar double-precision intrinsics such as
x86_sse41_round_sd was already handled by https://reviews.llvm.org/D82398,
but not their single-precision counterparts.

https://issuetracker.google.com/172238865

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D124871