Fix perf. of RCLASS_EXT_WRITABLE

FL_TEST -> FL_TEST_RAW
FL_SET  -> FL_SET_RAW

I was seeing bad performance on the ruby-bench getivar-module benchmark
when using yjit. This was with other changes in a branch, but changes
totally unrelated to accessing ivars on a class or using boxes. The
change to RCLASS_PRIME_CLASSEXT_WRITABLE_P was the one that made the
difference, but I changed a couple of other FL_SET uses as well. This
change reduced the benchmark runs from 60ms to 40ms.

Author: luke-gruber

internal/class.h

@@ -301,7 +301,7 @@ RCLASS_PRIME_CLASSEXT_WRITABLE_P(VALUE klass)
 {
     VM_ASSERT(klass != 0, "klass should be a valid object");
     VM_ASSERT_BOXABLE_TYPE(klass);
-    return FL_TEST(klass, RCLASS_PRIME_CLASSEXT_WRITABLE);
+    return FL_TEST_RAW(klass, RCLASS_PRIME_CLASSEXT_WRITABLE);
 }
 
 static inline void
@@ -310,10 +310,10 @@ RCLASS_SET_PRIME_CLASSEXT_WRITABLE(VALUE klass, bool writable)
     VM_ASSERT(klass != 0, "klass should be a valid object");
     VM_ASSERT_BOXABLE_TYPE(klass);
     if (writable) {
-        FL_SET(klass, RCLASS_PRIME_CLASSEXT_WRITABLE);
+        FL_SET_RAW(klass, RCLASS_PRIME_CLASSEXT_WRITABLE);
     }
     else {
-        FL_UNSET(klass, RCLASS_PRIME_CLASSEXT_WRITABLE);
+        FL_UNSET_RAW(klass, RCLASS_PRIME_CLASSEXT_WRITABLE);
     }
 }