JIT optimizations and refactoring (#675)

* CPU/Recompiler: Use rel32 call where possible for no-args

* JitCodeBuffer: Support using preallocated buffer

* CPU/Recompiler/AArch64: Use bl instead of blr for short branches

* CPU/CodeCache: Allocate recompiler buffer in program space

This means we don't need 64-bit moves for every call out of the
recompiler.

* GTE: Don't store as u16 and load as u32

* CPU/Recompiler: Add methods to emit global load/stores

* GTE: Convert class to namespace

* CPU/Recompiler: Call GTE functions directly

* Settings: Turn into a global variable

* GPU: Replace local pointers with global

* InterruptController: Turn into a global pointer

* System: Replace local pointers with global

* Timers: Turn into a global instance

* DMA: Turn into a global instance

* SPU: Turn into a global instance

* CDROM: Turn into a global instance

* MDEC: Turn into a global instance

* Pad: Turn into a global instance

* SIO: Turn into a global instance

* CDROM: Move audio FIFO to the heap

* CPU/Recompiler: Drop ASMFunctions

No longer needed since we have code in the same 4GB window.

* CPUCodeCache: Turn class into namespace

* Bus: Local pointer -> global pointers

* CPU: Turn class into namespace

* Bus: Turn into namespace

* GTE: Store registers in CPU state struct

Allows relative addressing on ARM.

* CPU/Recompiler: Align code storage to page size

* CPU/Recompiler: Fix relative branches on A64

* HostInterface: Local references to global

* System: Turn into a namespace, move events out

* Add guard pages

* Android: Fix build

src/common/jit_code_buffer.h

@@ -4,9 +4,14 @@
 class JitCodeBuffer
 {
 public:
-  JitCodeBuffer(u32 size = 64 * 1024 * 1024, u32 far_code_size = 0);
+  JitCodeBuffer();
+  JitCodeBuffer(u32 size, u32 far_code_size);
+  JitCodeBuffer(void* buffer, u32 size, u32 far_code_size, u32 guard_size);
   ~JitCodeBuffer();
 
+  bool Allocate(u32 size = 64 * 1024 * 1024, u32 far_code_size = 0);
+  bool Initialize(void* buffer, u32 size, u32 far_code_size = 0, u32 guard_size = 0);
+  void Destroy();
   void Reset();
 
   u8* GetFreeCodePointer() const { return m_free_code_ptr; }
@@ -25,16 +30,19 @@ public:
   static void FlushInstructionCache(void* address, u32 size);
 
 private:
-  u8* m_code_ptr;
-  u8* m_free_code_ptr;
-  u32 m_code_size;
-  u32 m_code_used;
+  u8* m_code_ptr = nullptr;
+  u8* m_free_code_ptr = nullptr;
+  u32 m_code_size = 0;
+  u32 m_code_used = 0;
 
-  u8* m_far_code_ptr;
-  u8* m_free_far_code_ptr;
-  u32 m_far_code_size;
-  u32 m_far_code_used;
+  u8* m_far_code_ptr = nullptr;
+  u8* m_free_far_code_ptr = nullptr;
+  u32 m_far_code_size = 0;
+  u32 m_far_code_used = 0;
 
-  u32 m_total_size;
+  u32 m_total_size = 0;
+  u32 m_guard_size = 0;
+  u32 m_old_protection = 0;
+  bool m_owns_buffer = false;
 };