Config: writable ext/Config/Makefile.PL

The src tarball changes ext/Config/Makefile.PL ro readonly.
Special case that in makerel, and check for -w Makefile.PL

Thanks to sten for reporting that. Fixes #142.

Author: Reini Urban

Porting/makerel

@@ -150,6 +150,7 @@ my @writables = qw(
     cpan/Devel-PPPort/module2.c
     cpan/Devel-PPPort/module3.c
     cpan/autodie/t/touch_me
+    ext/Config/Makefile.PL
     ext/Config/Config_xs.in
     ext/Config/Config_xs.out
     reentr.c

ext/Config/Makefile.PL

@@ -62,9 +62,12 @@ use ExtUtils::Command ();
     # touch what we plan for UNINST to be in the makefile
     @ARGV  = 'UNINST_'.($uninst ? '1' : '0');
     ExtUtils::Command::touch();
-    # now touch Makefile.PL so the above doesn't trigger a rebuild
-    @ARGV = 'Makefile.PL';
-    ExtUtils::Command::touch();
+    # now touch Makefile.PL so the above doesn't trigger a rebuild.
+    # note that with a src tarball, Makefile.PL is readonly
+    if (-w 'Makefile.PL') {
+        @ARGV = 'Makefile.PL';
+        ExtUtils::Command::touch();
+    }
     @ARGV = 'Makefile'; #we aren't inside WriteMakefile with open FH anymore
     ExtUtils::Command::touch();
     # if Makefile.PL and poison target are the same second, no rebuild happens