Fix pg_popcount_aarch64.c to build with ancient glibc releases.

Like commit 6d969ca68, except here we are mopping up after 519338ace.
(There are no other uses of <sys/auxv.h> in the tree, so we should
be done now.)

Reported-by: GaoZengqi <pgf00a@gmail.com>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAFmBtr3Av62-jBzdhFkDHXJF9vQmNtSnH2upwODjnRcsgdTytw@mail.gmail.com
Backpatch-through: 18

src/port/pg_popcount_aarch64.c

@@ -23,6 +23,10 @@
 
 #if defined(HAVE_ELF_AUX_INFO) || defined(HAVE_GETAUXVAL)
 #include <sys/auxv.h>
+/* Ancient glibc releases don't include the HWCAPxxx macros in sys/auxv.h */
+#if defined(__linux__) && !defined(HWCAP_SVE)
+#include <asm/hwcap.h>
+#endif
 #endif
 #endif