[NFC] Update return type of vec_popcnt to vector unsigned.

[amyk]

Summary

This patch updates the vec_popcnt builtins to return vector unsigned,
as defined by the Power Vector Intrinsics Programming Reference.
This patch is NFC and all existing tests pass.

[quinnp]

I think the commit message needs to be updated.

This patch updates the vec_popcnt builtins to take a signed int as the second parameter...

Should be: This patch updates the return type of the vec_popcnt builtins to vector unsigned...

Other than that, lgtm.

[kamaub]

This comment was removed by kamaub.

[kamaub]

Yeah this LGTM as well, accidentally commented without accepting a moment before.

clang/lib/Headers/altivec.h

 vec_cmplt(vector unsigned long long __a, vector unsigned long long __b) {
   return vec_cmpgt(__b, __a);
 }
 #endif
 
 #ifdef __POWER8_VECTOR__
 /* vec_popcnt */
 
-static __inline__ vector signed char __ATTRS_o_ai
+static __inline__ vector unsigned char __ATTRS_o_ai
 vec_popcnt(vector signed char __a) {
   return __builtin_altivec_vpopcntb(__a);
 }
 static __inline__ vector unsigned char __ATTRS_o_ai
 vec_popcnt(vector unsigned char __a) {
   return __builtin_altivec_vpopcntb(__a);
 }
-static __inline__ vector signed short __ATTRS_o_ai
+static __inline__ vector unsigned short __ATTRS_o_ai
 vec_popcnt(vector signed short __a) {
   return __builtin_altivec_vpopcnth(__a);
 }
 static __inline__ vector unsigned short __ATTRS_o_ai
 vec_popcnt(vector unsigned short __a) {
   return __builtin_altivec_vpopcnth(__a);
 }
-static __inline__ vector signed int __ATTRS_o_ai
+static __inline__ vector unsigned int __ATTRS_o_ai
 vec_popcnt(vector signed int __a) {
   return __builtin_altivec_vpopcntw(__a);
 }
 static __inline__ vector unsigned int __ATTRS_o_ai
 vec_popcnt(vector unsigned int __a) {
   return __builtin_altivec_vpopcntw(__a);
 }
-static __inline__ vector signed long long __ATTRS_o_ai
+static __inline__ vector unsigned long long __ATTRS_o_ai
 vec_popcnt(vector signed long long __a) {
   return __builtin_altivec_vpopcntd(__a);
 }
 static __inline__ vector unsigned long long __ATTRS_o_ai
 vec_popcnt(vector unsigned long long __a) {
   return __builtin_altivec_vpopcntd(__a);
 }