[Bug libfortran/78379] Processor-specific versions for matmul

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78379

--- Comment #17 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
On a hunch, this brings it back.

$(patsubst %.c,%.lo,$(notdir $(i_matmul_c))): AM_CFLAGS += -ffast-math
-ftree-vectorize -funroll-loops --param max-unroll-times=4 -march=native

So -march=native fixes it. not quite as fast as -prefer-avx128, but close
enough