Generate new OP_RESCUE; fix #3487

The old OP_RESCUE took one operand A, which specifies a class
to match with the exception. The new OP_RESCUE takes tree operands:

A: the register to hold exception
B: the matching exception; the match result will be stored here.
C: the continuation; if C is zero, the exception will be stored to R(A)
   otherwise, the value from R(A) is used as a exception.

Thus,
```ruby
begin
  raise "a"
rescue TypeError
  p 1
rescue RuntimeError
  p 2
end
```
will be compiled as
```
irep 0x557a06667aa0 nregs=4 nlocals=1 pools=1 syms=4 reps=0
file: /tmp/e.rb
2 000 OP_ONERR  005
2 001 OP_LOADSELF R1
2 002 OP_STRING R2  L(0)  ; "a"
2 003 OP_SEND R1  :raise  1
2 004 OP_JMP  022
3 005 OP_GETCONST R2  :TypeError
3 006 OP_RESCUE R1  R2
3 007 OP_JMPIF  R2  009
3 008 OP_JMP  013
4 009 OP_LOADSELF R1
4 010 OP_LOADI  R2  1
4 011 OP_SEND R1  :p  1
4 012 OP_JMP  023
5 013 OP_GETCONST R2 :RuntimeError
5 014 OP_RESCUE R1 R2  cont
5 015 OP_JMPIF  R2  017
5 016 OP_JMP  021
6 017 OP_LOADSELF R1
6 018 OP_LOADI  R2  2
6 019 OP_SEND R1  :p  1
6 020 OP_JMP  023
6 021 OP_RAISE  R1
6 022 OP_POPERR 1
6 023 OP_STOP
```

The new VM can accept old OP_RESCUE. The mruby compatible VM (namely
mruby/c) should be updated to support the new OP_RESCUE behavior.

mrbgems/mruby-compiler/core/codegen.c

@@ -1293,8 +1293,8 @@ codegen(codegen_scope *s, node *tree, int val)
       if (tree->car) {
         node *n2 = tree->car;
         int exc = cursp();
+        int cnt = 0;
 
-        genop(s, MKOP_ABC(OP_RESCUE, exc, 0, 0));
         push();
         while (n2) {
           node *n3 = n2->car;
@@ -1303,20 +1303,26 @@ codegen(codegen_scope *s, node *tree, int val)
           if (pos1) dispatch(s, pos1);
           pos2 = 0;
           do {
-            if (n4) {
-              codegen(s, n4->car, VAL);
-            }
-            else {
-              genop(s, MKOP_ABx(OP_GETCONST, cursp(), new_msym(s, mrb_intern_lit(s->mrb, "StandardError"))));
-              push();
-            }
-            genop(s, MKOP_AB(OP_MOVE, cursp(), exc));
-            pop();
             if (n4 && n4->car && (intptr_t)n4->car->car == NODE_SPLAT) {
+              if (cnt == 0) {
+                genop(s, MKOP_ABC(OP_RESCUE, exc, 0, cnt)); cnt = 1;
+              }
+              genop(s, MKOP_AB(OP_MOVE, cursp(), exc));
+              push();
+              codegen(s, n4->car, VAL);
+              pop_n(2);
               genop(s, MKOP_ABC(OP_SEND, cursp(), new_msym(s, mrb_intern_lit(s->mrb, "__case_eqq")), 1));
             }
             else {
-              genop(s, MKOP_ABC(OP_SEND, cursp(), new_msym(s, mrb_intern_lit(s->mrb, "===")), 1));
+              if (n4) {
+                codegen(s, n4->car, VAL);
+              }
+              else {
+                genop(s, MKOP_ABx(OP_GETCONST, cursp(), new_msym(s, mrb_intern_lit(s->mrb, "StandardError"))));
+                push();
+              }
+              pop();
+              genop(s, MKOP_ABC(OP_RESCUE, exc, cursp(), cnt)); cnt = 1;
             }
             tmp = genop(s, MKOP_AsBx(OP_JMPIF, cursp(), pos2));
             pos2 = tmp;
@@ -1788,11 +1794,7 @@ codegen(codegen_scope *s, node *tree, int val)
         genop(s, MKOP_A(OP_POPERR, 1));
         noexc = genop(s, MKOP_Bx(OP_JMP, 0));
         dispatch(s, onerr);
-<<<<<<< HEAD
-        genop(s, MKOP_AB(OP_RESCUE, exc, 0));
-=======
         genop(s, MKOP_ABC(OP_RESCUE, exc, 0, 0));
->>>>>>> 55d89bd... Enhance OP_RESCUE to take B operand fas matching exception; ref #3487
         genop(s, MKOP_A(OP_LOADF, exc));
         dispatch(s, noexc);
         loop_pop(s, NOVAL);