Allow unwinding of qvmcall64 call-stub for msvc/masm

qvmcall64 has its own custom calling convention due to pushing all non-volatile registers to the stack. The game uses set/longjmp which on Windows uses "RtlUnwindEx" to unwind the callstack. qvmcall64 cannot be unwound by default due to the custom calling convention. To allow unwinding, we need to add custom SEH unwind data to the function.

code/asm/vm_x86_64.asm

@@ -28,19 +28,35 @@
 ; Call to compiled code after setting up the register environment for the VM
 ; prototype:
 ; uint8_t qvmcall64(int *programStack, int *opStack, intptr_t *instructionPointers, byte *dataBase);
+;
+; This call-stub has its own custom calling convention due to pushing all non-volatile registers
+; to the stack. The game uses set/longjmp which on Windows uses "RtlUnwindEx" to unwind the callstack.
+; This function cannot be unwound by default due to the custom calling convention.
+; To allow unwinding, we need to add custom SEH unwind data to the function.
 
-qvmcall64 PROC
+qvmcall64 PROC FRAME
   push r12							; push all non-volatile registers to stack
+  .pushreg r12
   push r13
+  .pushreg r13
   push r14
+  .pushreg r14
   push r15
+  .pushreg r15
   push rdi
+  .pushreg rdi
   push rsi
+  .pushreg rsi
   push rbx
+  .pushreg rbx
   push rbp
+  .pushreg rbp
   
   ; need to save pointer in rcx so we can write back the programData value to caller
   push rcx
+  .pushreg rcx
+  
+  .endprolog						; custom unwind data ends here
 
   ; registers r8 and r9 have correct value already thanx to __fastcall
   xor rbx, rbx						; opStackOfs starts out being 0