regen/reentr.pl: Use hash instead of code conditionals

Fill this hash with the buffer sizes instead of using conditionals in
the code to do so.  This is in preparation for more variance in the
sizes, which would otherwise increase the number of conditionals

regen/reentr.pl

@@ -483,21 +483,28 @@ sub define {
 # The loop also contains a lot of intrinsic logic about groups of
 # functions (since functions of certain kind operate the same way).
 
+my %small_bufsizes = (
+                        asctime   => 26,
+                        ctime     => 26,
+                        setlocale => "REENTRANTSMALLSIZE",
+                        getlogin  => "REENTRANTSMALLSIZE",
+                        strerror  => "REENTRANTSMALLSIZE",
+                        ttyname   => "REENTRANTSMALLSIZE",
+                     );
+
 for my $func (@seenf) {
     my $FUNC = uc $func;
     my $ifdef = "#  ifdef HAS_${FUNC}_R\n";
     my $endif = "#  endif /* HAS_${FUNC}_R */\n\n";
     if (exists $seena{$func}) {
         my @p = @{$seena{$func}};
-        if ($func =~ /^(asctime|ctime|getlogin|setlocale|strerror|ttyname)$/) {
+        if (exists $small_bufsizes{$func}) {
             pushssif $ifdef;
             push @struct, <<EOF;
         char*	_${func}_buffer;
         size_t	_${func}_size;
 EOF
-            my $size = ($func =~ /^(asctime|ctime)$/)
-                       ? 26
-                       : "REENTRANTSMALLSIZE";
+            my $size = $small_bufsizes{$func};
             push @size, <<EOF;
         PL_reentrant_buffer->_${func}_size = $size;
 EOF