- For the debian/buster docker build (GCC 7/C++17) install and use the
system `catch` package; this also renames "COMPILER_PACKAGES" to
"EXTRA_PACKAGES" since it now contains a non-compiler package.
- Add a status message indicating the catch version being used for
compiling the embedded tests
- Simplify some bash code by using VAR+=" foo" to append (rather than
VAR="${VAR} foo"
- Fix CMAKE_INCLUDE_PATH appending: it was prepending the ':' but not
the existing $CMAKE_INCLUDE_PATH value and so would end up with
":/eigen-path" if CMAKE_INCLUDE_PATH was already set. (This wasn't
bug that was actually noticed since currently nothing else sets it).
Fixes a race condition when multiple threads try to acquire the GIL
before `detail::internals` have been initialized. `gil_scoped_release`
is now tasked with initializing `internals` (guaranteed single-threaded)
to ensure the safety of subsequent `acquire` calls from multiple threads.
At this point, there is only a single test for interpreter basics.
Apart from embedding itself, having a C++ test framework will also
benefit the C++-side features by allowing them to be tested directly.
