Move verification of Sema::MaximumAlignment to a .cpp file

Saves these transitive includes:

clang/include/clang/Sema/Sema.h

@@ -377,7 +377,7 @@ public:
   /// The maximum alignment, same as in llvm::Value. We duplicate them here
   /// because that allows us not to duplicate the constants in clang code,
   /// which we must to since we can't directly use the llvm constants.
-  /// The value is verified against llvm here: lib/CodeGen/CGValue.h
+  /// The value is verified against llvm here: lib/CodeGen/CGDecl.cpp
   ///
   /// This is the greatest alignment value supported by load, store, and alloca
   /// instructions, and global values.

clang/lib/CodeGen/CGDecl.cpp

@@ -31,6 +31,7 @@
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/CodeGen/CGFunctionInfo.h"
+#include "clang/Sema/Sema.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/GlobalVariable.h"
@@ -40,6 +41,9 @@
 using namespace clang;
 using namespace CodeGen;
 
+static_assert(clang::Sema::MaximumAlignment <= llvm::Value::MaximumAlignment,
+              "Clang max alignment greater than what LLVM supports?");
+
 void CodeGenFunction::EmitDecl(const Decl &D) {
   switch (D.getKind()) {
   case Decl::BuiltinTemplate:

clang/lib/CodeGen/CGValue.h

@@ -15,16 +15,12 @@
 #define LLVM_CLANG_LIB_CODEGEN_CGVALUE_H
 
 #include "clang/AST/ASTContext.h"
-#include "clang/Sema/Sema.h"
 #include "clang/AST/Type.h"
 #include "llvm/IR/Value.h"
 #include "llvm/IR/Type.h"
 #include "Address.h"
 #include "CodeGenTBAA.h"
 
-static_assert(clang::Sema::MaximumAlignment <= llvm::Value::MaximumAlignment,
-              "Clang max alignment greater than what LLVM supports?");
-
 namespace llvm {
   class Constant;
   class MDNode;