[StackMaps] Allow the target to pre-process the live-out mask

Some targets, PowerPC for example, have pseudo-registers (such as that used to
represent the rounding mode), that don't have DWARF register numbers or a
register class. These are used only for internal dependency tracking, and
should not appear in the recorded live-outs. This adds a callback allowing the
target to pre-process the live-out mask in order to remove these kinds of
registers so that the StackMaps code does not complain about them and/or
attempt to include them in the output.

This will be used by the PowerPC target in a future commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225805 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/StackMapLivenessAnalysis.cpp

@@ -123,5 +123,7 @@ uint32_t *StackMapLiveness::createRegisterMask() const {
   for (LivePhysRegs::const_iterator RI = LiveRegs.begin(), RE = LiveRegs.end();
        RI != RE; ++RI)
     Mask[*RI / 32] |= 1U << (*RI % 32);
+
+  TRI->adjustStackMapLiveOutMask(Mask);
   return Mask;
 }