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

Saves these transitive includes:
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index 589bd20..2946259 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/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:
diff --git a/clang/lib/CodeGen/CGValue.h b/clang/lib/CodeGen/CGValue.h
index 4d6c395..9fd07bd 100644
--- a/clang/lib/CodeGen/CGValue.h
+++ b/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;