Fix TestRubyOptions#test_enable for -DMJIT_FORCE_ENABLE

--enable=all didn't work when cppflags=-DMJIT_FORCE_ENABLE was given.

ruby.c

@@ -945,7 +945,12 @@ feature_option(const char *str, int len, void *arg, const unsigned int enable)
     if (NAME_MATCH_P(#bit, str, len)) {set |= mask = FEATURE_BIT(bit); FEATURE_FOUND;}
     EACH_FEATURES(SET_FEATURE, ;);
     if (NAME_MATCH_P("all", str, len)) {
+        // YJIT and MJIT cannot be enabled at the same time. We enable only YJIT for --enable=all.
+#ifdef MJIT_FORCE_ENABLE
+        mask &= ~(FEATURE_BIT(yjit));
+#else
         mask &= ~(FEATURE_BIT(jit));
+#endif
         goto found;
     }
 #if AMBIGUOUS_FEATURE_NAMES