revert 'char[] file' to 'char* file' on perl < 5.9

Prior commit ad2a648 changed 'char *'
to 'const char*' to match blead.  This broke 5.8.X, which expected a
non- constant file pointer in newXS.  Subsequent iterations had logic
that used 'const char*' for 5.9+ and 'char[]' for earlier perls, but
this broke mod_perl, which expects file to be an assignable pointer.

This commit reverts back to the 'char *' style used in perl 5.8.X.
This should finally put RT#48104 to bed.

lib/ExtUtils/ParseXS.pm

@@ -988,7 +988,7 @@ EOF
   #so `file' is unused
   print Q(<<"EOF") if $Full_func_name;
 ##if (PERL_REVISION == 5 && PERL_VERSION < 9)
-#    char file[] = __FILE__;
+#    char* file = __FILE__;
 ##else
 #    const char* file = __FILE__;
 ##endif