Implemented basic register allocation.

Mainly handles 'virtual' registers at the moment (eg current and last PC values, segment override status, etc).

src/codegen_backend_arm.c

@@ -15,6 +15,15 @@
 #include <windows.h>
 #endif
 
+int codegen_host_reg_list[CODEGEN_HOST_REGS] =
+{
+        REG_R4,
+        REG_R5,
+        REG_R6,
+//	REG_X22,
+//	REG_X23
+};
+
 void codegen_backend_init()
 {
         int c;