This is the first step in preparation for:
https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450

Fixes #118231 
- Updated the method name to `has_active_owner` in
`llvm-project/libc/src/__support/threads/linux/rwlock.h`
- Verified usage and updated all references to the method.
- Ran tests:
    - `check-llvm-unit`
    - `check-all`

- migrate more `-O3` to `${libc_opt_high_flag}`
- workaround a issue with `LLP64` in test. The overflow testing is
guarded by a constexpr but the literal overflow itself will still
trigger warnings.

Notice that for math smoke test, for some reasons, the
`${libc_opt_high_flag}` will be passed into `lld-link` which confuses
the linker so there are still some warnings leftover there. I can
investigate more when I have time.

Summary:
This patch implements 'getenv'. I was torn on how to implement this,
since realistically we only have access to this environment pointer in
the "loader" interface. An alternative would be to use an RPC call every
time, but I think that's overkill for what this will be used for. A
better solution is just to emit a common `DataEnvironment` that contains
all of the host visible resources to initialize. Right now this is the
`env_ptr`, `clock_freq`, and `rpc_client`.

I did this by making the `app.h` interface that Linux uses more general,
could possibly move that into a separate patch, but I figured it's
easier to see with the usage.

According to discussions on monthly meeting, we probably don't want to
cache `getpid` anymore. glibc removes their cache. bionic is hesitating
whether such cache is to be removed. `getpid` is async-signal-safe, so
we must make sure it always work.

However, for `gettid`, we have more freedom. Moreover, we are using
`gettid` to examine deadlock such that the performance penalty is not
negligible here. Thus, this patch is separated from previous patch to
provide only `tid` caching. It is much more simplified. Hopefully,
previous build issues can be resolved easily.

Summary:
This uses `internal::exit` which is not built in overlay mode, leading
to linker errors. Fix this to just use `assert.h`.