run-make: arm command wrappers with drop bombs
This PR is one in a series of cleanups to run-make tests and the run-make-support library.
### Summary
It's easy to forget to actually executed constructed command wrappers, e.g. `rustc().input("foo.rs")` but forget the `run()`, so to help catch these mistakes, we arm command wrappers with drop bombs on construction to force them to be executed by test code.
This PR also removes the `Deref`/`DerefMut` impl for our custom `Command` which derefs to `std::process::Command` because it can cause issues when trying to use a custom command:
```rs
htmldocck().arg().run()
```
fails to compile because the `arg()` is resolved to `std::process::Command::arg`, which returns `&mut std::process::Command` that doesn't have a `run()` command.
This PR also:
- Removes `env_var` on the `impl_common_helper` macro that was wrongly named and is a footgun (no users).
- Bumps the run-make-support library to version `0.1.0`.
- Adds a changelog to the support library.
### Details
Especially for command wrappers like `Rustc`, it's very easy to build up
a command invocation but forget to actually execute it, e.g. by using
`run()`. This commit adds "drop bombs" to command wrappers, which are
armed on command wrapper construction, and only defused if the command
is executed (through `run`, `run_fail`).
If the test writer forgets to execute the command, the drop bomb will
"explode" and panic with an error message. This is so that tests don't
silently pass with constructed-but-not-executed command wrappers.
This PR is best reviewed commit-by-commit.
try-job: x86_64-msvc
20ba13c38e