Piledriver arch (bdver2) use AMD64 optimizations or C code?

[Nate]

I am compiling GMP within the latest version of MinGW on a Windows 7 Pro
machine with a Piledriver CPU (A6-5400B).

Just running "configure" within Msys made GMP 6 compile with "-march=bdver2
-mtune=bdver2"

As this isn't on the list of GMP specially optimized architectures in the
documentation, is it just compiling from the generic C code? Do I need to
recompile and force the architecture and tuning to AMD64 for best
performance?

Thanks!