globvar.t: allow duplicate definitions of symbols

nm on AIX can list both local and global definitions for the same
variable, which meant the parsing would delete the first instance
from %exported, but then add the second to %unexported, failing the
test.

This didn't fail on AIX 5 because the default nm output didn't
match what the code expected when checking for PL_Yes, and so
the entire test script skipped.

Fixes #21623

t/porting/globvar.t

@@ -45,23 +45,29 @@ while (<$fh>) {
 
 close $fh or die "Problem running makedef.pl";
 
-my %unexported;
-
+# AIX can list a symbol as both a local and a global symbol
+# so collect all of the symbols *then* process them
+my %defined;
 foreach my $file (map {$_ . $Config{_o}} qw(globals regcomp)) {
     open $fh, '-|', $Config{nm}, "-P", $file
 	or die "Can't run nm $file";
 
     while (<$fh>) {
 	next unless /^_?(PL_\S+)${defined}/;
-	if (delete $exported{$1}) {
-	    note("Seen definition of $1");
-	    next;
-	}
-	++$unexported{$1};
+        $defined{$1} = 1;
     }
     close $fh or die "Problem running nm $file";
 }
 
+my %unexported;
+for my $name (sort keys %defined) {
+    if (delete $exported{$name}) {
+        note("Seen definition of $name");
+        next;
+    }
+    ++$unexported{$name};
+}
+
 unless ($Config{d_double_has_inf}) {
     $skip{PL_inf}++;
 }