BaseTools: Fixed regression issue for building !x86 builds

BaseTools: Fixed regression issue for building !x86 builds

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2134

This patch is to fix a build tool regression issue which
was introduced by commit e8449e1d8e.

In commit e8449e1d8e, build tool check the pcd before
filter out the irrelevant library instance.

The logic of evaluating the priority of the library class
resolutions was not changed.

Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Bob Feng <bob.c.feng@intel.com>
Tested-by: Michael D Kinney <michael.d.kinney@intel.com>
Acked-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>