Introduce a new signature for try_compile (and try_run) which removes
the `bindir` argument and requires the SOURCES tag. This will eventually
allow us to add other ways of providing sources, but also allows us to
change the behavior without breaking compatibility.
The old signature uses a special, but non-unique temporary location
inside the specified `bindir`, which conventionally is just the
project's build directory. The new signature unconditionally uses the a
unique temporary directory which is unconditionally within the project's
build directory (which is no longer separately specified). This ensures
that successive runs do not overwrite previous runs, will simplify
debugging, and should also, eventually, allow us to execute multiple
trials in parallel.
When the COPY_FILE operation fails optionally capture the error message
with a COPY_FILE_ERROR option instead of reporting the error
immediately. This gives callers a chance to do something else or report
the error.
Teach the RunCMake.try_compile test to cover bad argument combinations
involving COPY_FILE_ERROR. Teach the TryCompile test to cover the case
of a COPY_FILE error message captured by COPY_FILE_ERROR.
