rsync: fix build with musl

The rsync build tries to use IFUNC for SIMD optimizations on x86_64,
which has to be disabled for musl.

pkgs/applications/networking/sync/rsync/default.nix

···
     # disable the included zlib explicitly as it otherwise still compiles and
     # links them even.
     "--with-included-zlib=no"
+  ] ++ lib.optionals (stdenv.hostPlatform.isMusl && stdenv.hostPlatform.isx86_64) [
+    # fix `multiversioning needs 'ifunc' which is not supported on this target` error
+    "--disable-roll-simd"
   ];
 
   enableParallelBuilding = true;