Remove `do { ... } while(0)` hacks from `MRB_TRY` macros.

Because it can swallow `break` etc. if they are used in loops.

include/mruby/throw.h

@@ -15,9 +15,9 @@
 
 #if defined(MRB_ENABLE_CXX_EXCEPTION) && defined(__cplusplus)
 
-#define MRB_TRY(buf) do { try {
+#define MRB_TRY(buf) try {
 #define MRB_CATCH(buf) } catch(mrb_jmpbuf_impl e) { if (e != (buf)->impl) { throw e; }
-#define MRB_END_EXC(buf)  } } while(0)
+#define MRB_END_EXC(buf)  }
 
 #define MRB_THROW(buf) throw((buf)->impl)
 typedef mrb_int mrb_jmpbuf_impl;
@@ -34,9 +34,9 @@ typedef mrb_int mrb_jmpbuf_impl;
 #define MRB_LONGJMP longjmp
 #endif
 
-#define MRB_TRY(buf) do { if (MRB_SETJMP((buf)->impl) == 0) {
+#define MRB_TRY(buf) if (MRB_SETJMP((buf)->impl) == 0) {
 #define MRB_CATCH(buf) } else {
-#define MRB_END_EXC(buf) } } while(0)
+#define MRB_END_EXC(buf) }
 
 #define MRB_THROW(buf) MRB_LONGJMP((buf)->impl, 1);
 #define mrb_jmpbuf_impl jmp_buf