More __builtin_clz to std::countl_zero

Internal.h

@@ -2,6 +2,7 @@
 
 #include "ConflictSet.h"
 
+#include <bit>
 #include <cassert>
 #include <cstdint>
 #include <cstdlib>
@@ -83,7 +84,7 @@ constexpr inline int align_up(uint32_t unaligned, uint32_t align) {
 
 /// Returns the smallest power of two >= x
 [[maybe_unused]] constexpr inline uint32_t nextPowerOfTwo(uint32_t x) {
-  return x <= 1 ? 1 : 1 << (32 - __builtin_clz(x - 1));
+  return x <= 1 ? 1 : 1 << (32 - std::countl_zero(x - 1));
 }
 
 struct Arena::ArenaImpl {
@@ -277,7 +278,7 @@ inline uint32_t Arbitrary::bounded(uint32_t s) {
   if (s == 1) {
     return 0;
   }
-  switch (32 - __builtin_clz(s - 1)) {
+  switch (32 - std::countl_zero(s - 1)) {
   case 1:
   case 2:
   case 3: