https://github.com/steveicarus/iverilog/releases/tag/v12_0
Bump `iverilog` to 12.0, fixing two build failures:
1. autoconf now picks up on the unwrapped `x86_64-unknown-gnu-gcc` in
path that fails at configurePhase to link executables.
See: https://github.com/NixOS/nixpkgs/issues/21751
fix/hack: define the `{CC,CXX}_FOR_BUILD` variables.
2. buildPhase generates a `-Werror=format-security` error. Backport
the the upstream patch that fixed the warning very shortly after the
release was cut.
And in the process,
- use post-install tests from `.github/test.sh` and as a result,
remove the now unneeded clone of `ivtest`
- un-pin the verilog autoconf version
Signed-off-by: Jack Leightcap <jack@leightcap.com>
e97667163e