fix the clang CI build

Every module unit now includes the standard headers it uses. Declarations
reaching a unit only through an imported module's global module fragment
are reachable but not visible, so ADL misses the free operators older
libstdc++ declares beside a type - reproduced on ubuntu 24.04 (libstdc++
13), where gl/vao.cpp could not compare vector iterators.

Also drops a stale editor/editorSettings.hpp from the MSVC source list,
which broke the Windows configure step, silences the deliberate
include-in-purview warning in the glm wrapper, and removes GCC support:
clang or MSVC only.

editor/editorTerrainStreamer.cppm

@@ -17,6 +17,8 @@ http://mozilla.org/MPL/2.0/.
 // geometry GC reclaims their GPU memory). Heights are flat + a gentle procedural roll so streaming
 // is observable. Phase 2 will add 16-bit on-disk chunk paging, per-chunk flag bits and persistence.
 module;
+#include <cstddef>
+#include <utility>
 #include <cstdint>
 #include <map>
 #include <memory>