Fix check for trapping exit() calls in libpq

Commit e9bc0441f added an errorhint on the exit() check for libpq, but
accidentally changed the nm commandline to use -a instead of -A. These
options are similar enough to hide it in testing, but -a can also show
debugger symbols which isn't what we want. Fix by reverting the check
back to using -A again.

Reported-by: Anton Voloshin <a.voloshin@postgrespro.ru>
Discussion: https://postgr.es/m/bd2c8409-d6b3-5de9-ba0f-40c1381f630f@postgrespro.ru

src/interfaces/libpq/Makefile

@@ -115,7 +115,7 @@ backend_src = $(top_srcdir)/src/backend
 libpq-refs-stamp: $(shlib)
 ifneq ($(enable_coverage), yes)
 ifeq (,$(filter aix solaris,$(PORTNAME)))
-	@if nm -a -u $< 2>/dev/null | grep -v __cxa_atexit | grep exit; then \
+	@if nm -A -u $< 2>/dev/null | grep -v __cxa_atexit | grep exit; then \
 		echo 'libpq must not be calling any function which invokes exit'; exit 1; \
 	fi
 endif