Backport GCC 8 fixes

cmake/modules/HandleLLVMOptions.cmake

@@ -579,6 +579,11 @@ if (LLVM_ENABLE_WARNINGS AND (LLVM_COMPILER_IS_GCC_COMPATIBLE OR CLANG_CL))
   append_if(USE_NO_UNINITIALIZED "-Wno-uninitialized" CMAKE_CXX_FLAGS)
   append_if(USE_NO_MAYBE_UNINITIALIZED "-Wno-maybe-uninitialized" CMAKE_CXX_FLAGS)
 
+  # Disable -Wclass-memaccess, a C++-only warning from GCC 8 that fires on
+  # LLVM's ADT classes.
+  check_cxx_compiler_flag("-Wclass-memaccess" CXX_SUPPORTS_CLASS_MEMACCESS_FLAG)
+  append_if(CXX_SUPPORTS_CLASS_MEMACCESS_FLAG "-Wno-class-memaccess" CMAKE_CXX_FLAGS)
+
   # Check if -Wnon-virtual-dtor warns even though the class is marked final.
   # If it does, don't add it. So it won't be added on clang 3.4 and older.
   # This also catches cases when -Wnon-virtual-dtor isn't supported by

include/llvm/IR/GlobalValue.h

@@ -110,18 +110,12 @@ class GlobalValue : public Constant {
   unsigned IsDSOLocal : 1;
 
 private:
-  friend class Constant;
-
-  void maybeSetDsoLocal() {
-    if (hasLocalLinkage() ||
-        (!hasDefaultVisibility() && !hasExternalWeakLinkage()))
-      setDSOLocal(true);
-  }
-
   // Give subclasses access to what otherwise would be wasted padding.
   // (17 + 4 + 2 + 2 + 2 + 3 + 1 + 1) == 32.
   unsigned SubClassData : GlobalValueSubClassDataBits;
 
+  friend class Constant;
+
   void destroyConstantImpl();
   Value *handleOperandChangeImpl(Value *From, Value *To);
 
@@ -149,6 +143,12 @@ class GlobalValue : public Constant {
     llvm_unreachable("Fully covered switch above!");
   }
 
+  void maybeSetDsoLocal() {
+    if (hasLocalLinkage() ||
+        (!hasDefaultVisibility() && !hasExternalWeakLinkage()))
+      setDSOLocal(true);
+  }
+
 protected:
   /// The intrinsic ID for this subclass (which must be a Function).
   ///