Fix build with LLVM 13 on ppc64le

/wrkdirs/usr/ports/graphics/opencv/work/opencv-4.5.5/modules/core/include/opencv2/core/vsx_utils.hpp:352:12: warning: 'vec_permi' macro redefined [-Wmacro-redefined]
#   define vec_permi(a, b, c) vec_xxpermdi(b, a, (3 ^ (((c) & 1) << 1 | (c) >> 1)))
           ^
/usr/lib/clang/13.0.0/include/altivec.h:13077:9: note: previous definition is here
#define vec_permi(__a, __b, __c)                                               \
        ^
/wrkdirs/usr/ports/graphics/opencv/work/opencv-4.5.5/modules/core/include/opencv2/core/vsx_utils.hpp:370:25: error: redefinition of 'vec_promote'
VSX_FINLINE(vec_dword2) vec_promote(long long a, int b)
                        ^
/usr/lib/clang/13.0.0/include/altivec.h:14604:1: note: previous definition is here
vec_promote(signed long long __a, int __b) {
^
/wrkdirs/usr/ports/graphics/opencv/work/opencv-4.5.5/modules/core/include/opencv2/core/vsx_utils.hpp:377:26: error: redefinition of 'vec_promote'
VSX_FINLINE(vec_udword2) vec_promote(unsigned long long a, int b)
                         ^
/usr/lib/clang/13.0.0/include/altivec.h:14611:1: note: previous definition is here
vec_promote(unsigned long long __a, int __b) {
^
/wrkdirs/usr/ports/graphics/opencv/work/opencv-4.5.5/modules/core/include/opencv2/core/hal/intrin_vsx.hpp:1045:22: error: call to 'vec_rsqrt' is ambiguous
{ return v_float32x4(vec_rsqrt(x.val)); }
                     ^~~~~~~~~
/usr/lib/clang/13.0.0/include/altivec.h:8472:34: note: candidate function
static vector float __ATTRS_o_ai vec_rsqrt(vector float __a) {
                                 ^
/wrkdirs/usr/ports/graphics/opencv/work/opencv-4.5.5/modules/core/include/opencv2/core/vsx_utils.hpp:362:29: note: candidate function
    VSX_FINLINE(vec_float4) vec_rsqrt(const vec_float4& a)
                            ^
/wrkdirs/usr/ports/graphics/opencv/work/opencv-4.5.5/modules/core/include/opencv2/core/hal/intrin_vsx.hpp:1047:22: error: call to 'vec_rsqrt' is ambiguous
{ return v_float64x2(vec_rsqrt(x.val)); }
                     ^~~~~~~~~
/usr/lib/clang/13.0.0/include/altivec.h:8477:35: note: candidate function
static vector double __ATTRS_o_ai vec_rsqrt(vector double __a) {
                                  ^
/wrkdirs/usr/ports/graphics/opencv/work/opencv-4.5.5/modules/core/include/opencv2/core/vsx_utils.hpp:365:30: note: candidate function
    VSX_FINLINE(vec_double2) vec_rsqrt(const vec_double2& a)
                             ^
1 warning and 4 errors generated.

The specific functions were added to altivec.h in LLVM's 1ff93618e58df210def48d26878c20a1b414d900, c3da07d216dd20fbdb7302fd085c0a59e189ae3d and 10cc5bcd868c433f9a781aef82178b04e98bd098.

modules/core/include/opencv2/core/vsx_utils.hpp

@@ -324,6 +324,7 @@ VSX_IMPL_1RG(vec_udword2, vec_float4,  xvcvspuxds, vec_ctulo)
 #define VSX_IMPL_CONVERT(rt, rg, fnm) \
 VSX_FINLINE(rt) fnm(const rg& a) { return __builtin_convertvector(a, rt); }
 
+#ifndef vec_permi
 #if __clang_major__ < 5
 // implement vec_permi in a dirty way
 #   define VSX_IMPL_CLANG_4_PERMI(Tvec)                                                 \
@@ -351,12 +352,14 @@ VSX_FINLINE(rt) fnm(const rg& a) { return __builtin_convertvector(a, rt); }
 // vec_xxpermdi is missing little-endian supports in clang 4 just like gcc4
 #   define vec_permi(a, b, c) vec_xxpermdi(b, a, (3 ^ (((c) & 1) << 1 | (c) >> 1)))
 #endif // __clang_major__ < 5
+#endif
 
 // shift left double by word immediate
 #ifndef vec_sldw
 #   define vec_sldw vec_xxsldwi
 #endif
 
+#if __clang_major__ < 13
 // Implement vec_rsqrt since clang only supports vec_rsqrte
 #ifndef vec_rsqrt
     VSX_FINLINE(vec_float4) vec_rsqrt(const vec_float4& a)
@@ -380,6 +383,7 @@ VSX_FINLINE(vec_udword2) vec_promote(unsigned long long a, int b)
     ret[b & 1] = a;
     return ret;
 }
+#endif
 
 // vec_popcnt should return unsigned but clang has different thought just like gcc in vec_vpopcnt
 #define VSX_IMPL_POPCNTU(Tvec, Tvec2, ucast)   \