EmulatorPkg: Clear DLINK_XIPFLAGS

Clear DLINK_XIPFLAGS to disable use of alignment flags
for all tool chains. Setting alignment flags other than
the OS application defaults are not required for
EmulatorPkg builds.

Add and/or clarify comments to explain the overrides to
the default firmware build configurations required for
EmulatorPkg.dsc builds.

Align Mingw CLANGDWARF to GCC by moving the application
libraries into DLINK2_FLAGS.

Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>