util/mkerr.pl: Add an inclusion of symhacks.h in all error files

This does no harm, and ensures that the inclusion isn't mistakenly
removed in the generated *err.h where it's actually needed.

Reviewed-by: Nicola Tuveri <nic.tuv@gmail.com>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from openssl#8397)

include/openssl/cryptoerr.h

@@ -15,8 +15,6 @@
 extern "C"
 # endif
 
-# include <openssl/symhacks.h>
-
 int ERR_load_CRYPTO_strings(void);
 
 /*

util/mkerr.pl

@@ -417,9 +417,7 @@ sub help
 &phase("Writing files");
 my $newstate = 0;
 foreach my $lib ( keys %errorfile ) {
-    if ( ! $fnew{$lib} && ! $rnew{$lib} ) {
-        next unless $rebuild;
-    }
+    next if ! $fnew{$lib} && ! $rnew{$lib} && ! $rebuild;
     next if scalar keys %modules > 0 && !$modules{$lib};
     next if $nowrite;
     print STDERR "$lib: $fnew{$lib} new functions\n" if $fnew{$lib};
@@ -455,6 +453,10 @@ sub help
 #ifndef HEADER_${lib}ERR_H
 # define HEADER_${lib}ERR_H
 
+# ifndef HEADER_SYMHACKS_H
+#  include <openssl/symhacks.h>
+# endif
+
 EOF
     if ( $internal ) {
         # Declare the load function because the generate C file