[CodeGenSchedule][NFC] Always emit ProcResourceUnits.

[courbet]

Summary

Right now only the ProcResourceUnits that are directly referenced by
instructions are emitted. This change emits all of them, so that
analysis passes can use the information.
This has no functional impact. It typically adds a few entries (e.g. 4
for X86/haswell) to the generated ProcRes table.

utils/TableGen/CodeGenSchedule.cpp

void CodeGenSchedModels::collectProcResources() {
   RecVec ProcResGroups = Records.getAllDerivedDefinitions("ProcResGroup");
   for (Record *PRG : ProcResGroups) {
     if (!PRG->getValueInit("SchedModel")->isComplete())
       continue;
     CodeGenProcModel &PM = getProcModel(PRG->getValueAsDef("SchedModel"));
     if (!is_contained(PM.ProcResourceDefs, PRG))
       PM.ProcResourceDefs.push_back(PRG);
   }
+  // Add ProcResourceUnits unconditionally.
+  for (Record *PRU : Records.getAllDerivedDefinitions("ProcResourceUnits")) {
+    if (!PRU->getValueInit("SchedModel")->isComplete())
+      continue;
+    CodeGenProcModel &PM = getProcModel(PRU->getValueAsDef("SchedModel"));
+    if (!is_contained(PM.ProcResourceDefs, PRU))
+      PM.ProcResourceDefs.push_back(PRU);
+  }
   // Finalize each ProcModel by sorting the record arrays.
   for (CodeGenProcModel &PM : ProcModels) {
     std::sort(PM.WriteResDefs.begin(), PM.WriteResDefs.end(),
               LessRecord());
     std::sort(PM.ReadAdvanceDefs.begin(), PM.ReadAdvanceDefs.end(),
               LessRecord());
     std::sort(PM.ProcResourceDefs.begin(), PM.ProcResourceDefs.end(),
               LessRecord());