Define separate enum values for rotation data in both the high bits,
where it is usually kept, and the low bits, where it is sometimes used
for math or comparisons.
Define an enum value to represent the composite of the index and the
rotation, since the composite is not suitable for use as an array
subscript. Add helper functions to extract the component pieces.
gcc-4.9 support is now difficult to test due to system libraries linking
to newer symbols. gcc-4.9 is unsupported upstream, as are gcc-5 and
gcc-6. Raise the minimum required gcc version to the minimum version
supported upstream.
Debian Jessie shipped gcc-4.9.2, and support for this target was the
primary motivator for retaining gcc-4.9 support. Jessie ended regular
support in June 2018, and will end Long Term Support in June 2020. It
seems unlikely that Jessie would receive a snapshot build of Rebirth in
the months it has left.
Debian Stretch shipped gcc-6, but is currently considered "oldstable"
and has been superseded by Debian Buster. Further, Debian Stretch
provides a package for gcc-7, so Stretch users can still build Rebirth
using only packages available from the package manager.
In multiplayer, the host sends a destroy message for both sides of the
wall. `do_exploding_wall_frame` processes both, but
`num_exploding_walls` is only decreased by 1, causing an assertion
failure at the end. Remove the assertion, since the wall does not
explode instantly on join, despite being marked as WALL_EXPLODING.
gcc-4.9 rejects defining a class with a reference member and no
constructor, even though the use of the class uses a
brace-initialization expression to set the reference at construction
time.
Fixes: fa654324ad ("Pass context to wall.cpp:cwframe, cw_removal_predicate")
