[Serialization] Move LLVM_NORETURN to declaration start

On Windows, `LLVM_NORETURN` expands to `__declspec(noreturn)`, which
must be placed at the start of the declaration. All other possible
expansions of that macro should also support being placed at the start
of the declaration.

Author: smeenai

include/swift/Serialization/ModuleFile.h

@@ -434,7 +434,7 @@ class ModuleFile
 
   /// Emits one last diagnostic, logs the error, and then aborts for the stack
   /// trace.
-  void fatal(llvm::Error error) LLVM_ATTRIBUTE_NORETURN;
+  LLVM_ATTRIBUTE_NORETURN void fatal(llvm::Error error);
 
   ASTContext &getContext() const {
     assert(FileContext && "no associated context yet");