Fix __attribute__((target(...))) usage.

The commonly supported way to specify multiple target options is to
surround the entire list with quotes and to use a comma (with no
extra spaces) as the delimiter.

Oversight in commit f78667bd91.

Discussion: https://postgr.es/m/Zy0jya8nF8CPpv3B%40nathan

config/c-compiler.m4

@@ -733,7 +733,7 @@ AC_DEFUN([PGAC_AVX512_POPCNT_INTRINSICS],
 AC_CACHE_CHECK([for _mm512_popcnt_epi64], [Ac_cachevar],
 [AC_LINK_IFELSE([AC_LANG_PROGRAM([#include <immintrin.h>
     #if defined(__has_attribute) && __has_attribute (target)
-    __attribute__((target("avx512vpopcntdq","avx512bw")))
+    __attribute__((target("avx512vpopcntdq,avx512bw")))
     #endif
     static int popcount_test(void)
     {

configure

@@ -17324,7 +17324,7 @@ else
 /* end confdefs.h.  */
 #include <immintrin.h>
     #if defined(__has_attribute) && __has_attribute (target)
-    __attribute__((target("avx512vpopcntdq","avx512bw")))
+    __attribute__((target("avx512vpopcntdq,avx512bw")))
     #endif
     static int popcount_test(void)
     {

meson.build

@@ -2184,7 +2184,7 @@ if host_cpu == 'x86_64'
 #include <immintrin.h>
 
 #if defined(__has_attribute) && __has_attribute (target)
-__attribute__((target("avx512vpopcntdq","avx512bw")))
+__attribute__((target("avx512vpopcntdq,avx512bw")))
 #endif
 int main(void)
 {

src/port/pg_popcount_avx512.c

@@ -106,7 +106,7 @@ pg_popcount_avx512_available(void)
  * pg_popcount_avx512
  *		Returns the number of 1-bits in buf
  */
-pg_attribute_target("avx512vpopcntdq", "avx512bw")
+pg_attribute_target("avx512vpopcntdq,avx512bw")
 uint64
 pg_popcount_avx512(const char *buf, int bytes)
 {
@@ -162,7 +162,7 @@ pg_popcount_avx512(const char *buf, int bytes)
  * pg_popcount_masked_avx512
  *		Returns the number of 1-bits in buf after applying the mask to each byte
  */
-pg_attribute_target("avx512vpopcntdq", "avx512bw")
+pg_attribute_target("avx512vpopcntdq,avx512bw")
 uint64
 pg_popcount_masked_avx512(const char *buf, int bytes, bits8 mask)
 {