[OpenMPIRBuilder] Check GV type instead of pointee type (NFC)

Change the assertion to check the value type instead of the pointee
type. To facilitate this, store GlobalVariable* instead of Constant*
in the map.

Author: nikic

llvm/include/llvm/Frontend/OpenMP/OMPIRBuilder.h

@@ -1469,7 +1469,7 @@ class OpenMPIRBuilder {
   /// <critical_section_name> + ".var" for "omp critical" directives; 2)
   /// <mangled_name_for_global_var> + ".cache." for cache for threadprivate
   /// variables.
-  StringMap<Constant*, BumpPtrAllocator> InternalVars;
+  StringMap<GlobalVariable *, BumpPtrAllocator> InternalVars;
 
   /// Computes the size of type in bytes.
   Value *getSizeInBytes(Value *BasePtr);

llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp

@@ -4410,8 +4410,7 @@ OpenMPIRBuilder::getOrCreateInternalVariable(Type *Ty, const StringRef &Name,
                                              unsigned AddressSpace) {
   auto &Elem = *InternalVars.try_emplace(Name, nullptr).first;
   if (Elem.second) {
-    assert(cast<PointerType>(Elem.second->getType())
-               ->isOpaqueOrPointeeTypeMatches(Ty) &&
+    assert(Elem.second->getValueType() == Ty &&
            "OMP internal variable has different type than requested");
   } else {
     // TODO: investigate the appropriate linkage type used for the global
@@ -4426,7 +4425,7 @@ OpenMPIRBuilder::getOrCreateInternalVariable(Type *Ty, const StringRef &Name,
     Elem.second = GV;
   }
 
-  return cast<GlobalVariable>(&*Elem.second);
+  return Elem.second;
 }
 
 Value *OpenMPIRBuilder::getOMPCriticalRegionLock(StringRef CriticalName) {