[Misc] Fix Some Warnings on Clang Build with Windows + Adding constexpr

src/xenia/cpu/backend/x64/x64_code_cache_win.cc

@@ -92,7 +92,7 @@ typedef struct _UNWIND_INFO {
 
 // Size of unwind info per function.
 // TODO(benvanik): move this to emitter.
-static const uint32_t kUnwindInfoSize =
+static constexpr uint32_t kUnwindInfoSize =
     sizeof(UNWIND_INFO) + (sizeof(UNWIND_CODE) * (6 - 1));
 
 class Win32X64CodeCache : public X64CodeCache {

src/xenia/cpu/backend/x64/x64_emitter.cc

@@ -1243,7 +1243,7 @@ void* X64Emitter::FindQwordConstantOffset(uint64_t qwordvalue) {
 }
 // First location to try and place constants.
 static constexpr uintptr_t kConstDataLocation = 0x20000000;
-static const uintptr_t kConstDataSize = sizeof(xmm_consts);
+static constexpr uintptr_t kConstDataSize = sizeof(xmm_consts);
 
 // Increment the location by this amount for every allocation failure.
 static constexpr uintptr_t kConstDataIncrement = 0x00001000;

src/xenia/cpu/backend/x64/x64_emitter.h

@@ -227,8 +227,8 @@ class X64Emitter : public Xbyak::CodeGenerator {
   //            xmm0-2
   // Available: rbx, r10-r15
   //            xmm4-xmm15 (save to get xmm3)
-  static const int GPR_COUNT = 7;
-  static const int XMM_COUNT = 12;
+  static constexpr int GPR_COUNT = 7;
+  static constexpr int XMM_COUNT = 12;
   static constexpr size_t kStashOffset = 32;
   static void SetupReg(const hir::Value* v, Xbyak::Reg8& r) {
     auto idx = gpr_reg_map_[v->reg.index];

src/xenia/cpu/backend/x64/x64_op.h

@@ -123,7 +123,7 @@ struct OpBase {};
 
 template <typename T, KeyType KEY_TYPE>
 struct Op : OpBase {
-  static const KeyType key_type = KEY_TYPE;
+  static constexpr KeyType key_type = KEY_TYPE;
 };
 
 struct VoidOp : Op<VoidOp, KEY_TYPE_X> {