regcomp.c: Use single_1bit_pos()

This new function replaces the code in this file.  The new function will
operate on 64-bit words, whereas only 32 bits are required here.  But
there should be no slowdown.

regcomp.c

@@ -19398,17 +19398,8 @@ S_optimize_regclass(pTHX_
             bool already_inverted;
             bool are_equivalent;
 
-            /* Compute which bit is set, which is the same thing as, e.g.,
-             * ANYOF_CNTRL.  From
-             * https://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn
-             * */
-            static const int MultiplyDeBruijnBitPosition2[32] = {
-                0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
-                31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
-                };
 
-            namedclass = MultiplyDeBruijnBitPosition2[(posixl
-                                                      * 0x077CB531U) >> 27];
+            namedclass = single_1bit_pos(posixl);
             classnum = namedclass_to_classnum(namedclass);
 
             /* The named classes are such that the inverted number is one