BaseTools: Fix DevicePath GNUmakefile for macOS

On macOS, /usr/bin/gcc is clang, and so doesn't have
the -Wno-error=stringop-overflow flag that was added
for gcc 12.
Update the GNUmakefile for DevicePath to skip setting
that on macOS.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
1 file changed