gnu: cross-base: Add mingw-w64 specific binutils patches.

gnu: cross-base: Add mingw-w64 specific binutils patches.

These patches were originally found at the debian mingw-w64 team's
binutils repo, and should improve the reproducibility of our mingw-w64
toolchain.

* gnu/packages/patches/binutils-mingw-w64-reproducible-import-libraries.patch:
New file.
* gnu/packages/patches/binutils-mingw-w64-specify-timestamp.patch:
New file.
* gnu/local.mk (dist_patch_DATA): Update accordingly.
* gnu/packages/cross-base.scm (cross-binutils): Apply relevant patches
if target is mingw-w64.
(package-with-extra-patches): New procedure.