chore: Enable more compiler warnings in debug mode

[paleolimbot]

This PR fixes some compiler warnings and enables more of them in a normal debug build such that they are spotted early.

[jorisvandenbossche]

Starting with this commit, I get build errors on conda if enabling DEBUG mode:

[ 33%] Building CXX object CMakeFiles/s2geography.dir/src/s2geography/build.cc.o
In file included from /home/joris/conda/envs/spherely-dev/include/absl/container/inlined_vector.h:53,
                 from /home/joris/conda/envs/spherely-dev/include/absl/status/internal/status_internal.h:26,
                 from /home/joris/conda/envs/spherely-dev/include/absl/status/status.h:66,
                 from /home/joris/conda/envs/spherely-dev/include/s2/s2coder.h:23,
                 from /home/joris/conda/envs/spherely-dev/include/s2/s2point.h:27,
                 from /home/joris/conda/envs/spherely-dev/include/s2/s1angle.h:28,
                 from /home/joris/conda/envs/spherely-dev/include/s2/s2cell_id.h:43,
                 from /home/joris/scipy/repos/s2geography/src/s2geography/geography.h:4,
                 from /home/joris/scipy/repos/s2geography/src/s2geography/distance.h:4,
                 from /home/joris/scipy/repos/s2geography/src/s2geography/distance.cc:2:
In member function 'void absl::lts_20240116::inlined_vector_internal::Storage<T, N, A>::MemcpyFrom(const absl::lts_20240116::inlined_vector_internal::Storage<T, N, A>&) [with T = S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry; long unsigned int N = 16; A = std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry>]',
    inlined from 'void absl::lts_20240116::InlinedVector<T, N, A>::MoveAssignment(MemcpyPolicy, absl::lts_20240116::InlinedVector<T, N, A>&&) [with T = S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry; long unsigned int N = 16; A = std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry>]' at /home/joris/conda/envs/spherely-dev/include/absl/container/inlined_vector.h:856:24,
    inlined from 'absl::lts_20240116::InlinedVector<T, N, A>& absl::lts_20240116::InlinedVector<T, N, A>::operator=(absl::lts_20240116::InlinedVector<T, N, A>&&) [with T = S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry; long unsigned int N = 16; A = std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry>]' at /home/joris/conda/envs/spherely-dev/include/absl/container/inlined_vector.h:548:21,
    inlined from 'std::priority_queue<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, absl::lts_20240116::InlinedVector<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, 16, std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >, std::less<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >& std::priority_queue<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, absl::lts_20240116::InlinedVector<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, 16, std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >, std::less<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >::operator=(std::priority_queue<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, absl::lts_20240116::InlinedVector<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, 16, std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >, std::less<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >&&)' at /home/joris/conda/envs/spherely-dev/lib/gcc/x86_64-conda-linux-gnu/12.4.0/include/c++/bits/stl_queue.h:498:11,
    inlined from 'void S2ClosestEdgeQueryBase<Distance>::FindClosestEdgesOptimized() [with Distance = S2MinDistance]' at /home/joris/conda/envs/spherely-dev/include/s2/s2closest_edge_query_base.h:666:14:
/home/joris/conda/envs/spherely-dev/include/absl/container/internal/inlined_vector.h:532:5: error: '<unnamed>.std::priority_queue<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, absl::lts_20240116::InlinedVector<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, 16, std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >, std::less<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >::c.absl::lts_20240116::InlinedVector<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, 16, std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >::storage_.absl::lts_20240116::inlined_vector_internal::Storage<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry, 16, std::allocator<S2ClosestEdgeQueryBase<S2MinDistance>::QueueEntry> >::data_' may be used uninitialized [-Werror=maybe-uninitialized]
  532 |     data_ = other_storage.data_;
      |     ^~~~~

Something related to the abseil conda package might not like all of those compiler directives?

[paleolimbot]

Probably. I'll make those compiler warning checks opt-in (Google famously doesn't care about them).