[builtins] Flag __builtin_cl* functions as `static`

[alexcrichton]

Summary

Without these then all of these functions show up in all object files which include int_lib.h on Windows. This'll help prevent duplicate symbols by ensuring they're not exported.

[whitequark]

I'm not the one to sign off on this diff, sorry.

lib/builtins/int_lib.h

 #if defined(_MSC_VER) && !defined(__clang__)
 #include <intrin.h>
 
-uint32_t __inline __builtin_ctz(uint32_t value) {
+static uint32_t __inline __builtin_ctz(uint32_t value) {
   unsigned long trailing_zero = 0;
   if (_BitScanForward(&trailing_zero, value))
     return trailing_zero;
   return 32;
 }
 
-uint32_t __inline __builtin_clz(uint32_t value) {
+static uint32_t __inline __builtin_clz(uint32_t value) {
   unsigned long leading_zero = 0;
   if (_BitScanReverse(&leading_zero, value))
     return 31 - leading_zero;

 }
 
 #if defined(_M_ARM) || defined(_M_X64)
-uint32_t __inline __builtin_clzll(uint64_t value) {
+static uint32_t __inline __builtin_clzll(uint64_t value) {
   unsigned long leading_zero = 0;
   if (_BitScanReverse64(&leading_zero, value))
     return 63 - leading_zero;
   return 64;
 }
 #else
-uint32_t __inline __builtin_clzll(uint64_t value) {
+static uint32_t __inline __builtin_clzll(uint64_t value) {
   if (value == 0)
     return 64;
   uint32_t msh = (uint32_t)(value >> 32);