* gnu/packages/zig.scm (zig-0.9)[source]: Add patch.
[arguments]: Skip tests when building for riscv64-linux. When building
for riscv64-linux add a phase to adjust the tests.
* gnu/packages/patches/zig-0.9-riscv-support.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.