patching r/o files => failure on Linux

[Aleksey Cheusov <cheusov%tut.by@localhost>]

In some of pkgsrc packages read-only files (0444 permissions) are
patched.  As a result patch phase fails on Linux. For example,
this is how devel/libtool-base fails to build.

   => Applying pkgsrc patches for libtool-base-2.2.6bnb4
   File libltdl/config/ltmain.sh is read-only; refusing to patch
   1 out of 1 hunk ignored -- saving rejects to file 
libltdl/config/ltmain.sh.rej
   Patch /srv/pkgsrc/devel/libtool-base/../libtool/patches/patch-ac failed
   ERROR: Patching failed due to modified or broken patch file(s):
   ERROR:  /srv/pkgsrc/devel/libtool-base/../libtool/patches/patch-ac

Workaround shown below fixes the problem.

   pre-patch:
        chmod +w ${WRKSRC}/libltdl/config/ltmain.sh

Is there a better way to fix such problems?

-- 
Best regards, Aleksey Cheusov.