REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2221
The command used by multiple thread genffs feature in makefile
for testing if file exist is generated based on the toolchain family.
It should be based on the OS type.
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
a1f94045ff