[clang][modules] Over-align the `Module` class

This makes `llvm::PointerIntPair<Module *, 3>` from f35230ae work across platforms.

Reviewed By: srj

Differential Revision: https://reviews.llvm.org/D134653

clang/include/clang/Basic/Module.h

@@ -93,7 +93,9 @@ struct ASTFileSignature : std::array<uint8_t, 20> {
 };
 
 /// Describes a module or submodule.
-class Module {
+///
+/// Aligned to 8 bytes to allow for llvm::PointerIntPair<Module *, 3>.
+class alignas(8) Module {
 public:
   /// The name of this module.
   std::string Name;