zig.h: enable popcount, ctz, clz

- netbsd and dragonfly are slow to upgrade system compiler versions
- they lack support for preprocessor tests like `__has_builtin`
- yet they have support for popcount, ctz, clz
- for now, just assume __builtin_{clz,ctz,popcount} is available
- tests for these builtins are going to be important wrt other archs

*** THIS IS TEMPORARY AND A BETTER SOLUTION IS NEEDED ***

Author: mikdusan

lib/zig.h

@@ -917,7 +917,6 @@ typedef zig_c_ulong zig_Builtin64;
 typedef zig_c_ulonglong zig_Builtin64;
 #endif
 
-#if zig_has_builtin(clz)
 #define zig_builtin_clz(w) \
     static inline zig_u8 zig_clz_u##w(zig_u##w val, zig_u8 bits) { \
         if (val == 0) return bits; \
@@ -931,9 +930,7 @@ zig_builtin_clz(8)
 zig_builtin_clz(16)
 zig_builtin_clz(32)
 zig_builtin_clz(64)
-#endif
 
-#if zig_has_builtin(ctz)
 #define zig_builtin_ctz(w) \
     static inline zig_u8 zig_ctz_u##w(zig_u##w val, zig_u8 bits) { \
         if (val == 0) return bits; \
@@ -947,9 +944,7 @@ zig_builtin_ctz(8)
 zig_builtin_ctz(16)
 zig_builtin_ctz(32)
 zig_builtin_ctz(64)
-#endif
 
-#if zig_has_builtin(popcount)
 #define zig_builtin_popcount(w) \
     static inline zig_u8 zig_popcount_u##w(zig_u##w val, zig_u8 bits) { \
         (void)bits; \
@@ -964,7 +959,6 @@ zig_builtin_popcount(8)
 zig_builtin_popcount(16)
 zig_builtin_popcount(32)
 zig_builtin_popcount(64)
-#endif
 
 static inline zig_u8 zig_byte_swap_u8(zig_u8 val, zig_u8 bits) {
     return zig_wrap_u8(val >> (8 - bits), bits);