Currently Linux builds override the default BUILD mode by putting it in
the generated config. That makes it sticky for manual runs of make,
which is inconsistent with how other platforms work.
Instead, pass the build mode as a command-line override, the same way
someone would if building directly with make. This makes the flow of
controlling the mode less confusing.
Fixes#41528
When building in profile or release mode on desktop, add a prominent
warning that it's actually a debug build. This is to help address issues
with people being unaware of the current state of builds due to
following third-party guides rather than official documentation.
macOS is not included since PRs are in flight for macOS release support.
