MdePkg/BaseSynchronizationLib GCC: simplify IA32 InternalSyncCompareExchange64()

MdePkg/BaseSynchronizationLib GCC: simplify IA32 InternalSyncCompareExchange64()

The IA32 variant of InternalSyncCompareExchange64() is correct, but we can
simplify it. We don't need to load the lower 32 bits of ExchangeValue into
EBX in two steps (first into a general register, then into EBX); we can
ask GCC to populate EBX like that itself.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1208
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>