faster ASSIMP build

Disabled most of the importer/exporter formats by default, for faster
development and CI.

Note that you may need to CMakeCache.txt for this to take effect, as the
options might be cached.

CMakeLists.txt

@@ -28,6 +28,17 @@ set(GLM_INC_DIR ${PROJECT_SOURCE_DIR}/third_party/glm)
 
 set_property(CACHE THRUST_BACKEND PROPERTY STRINGS CUDA OMP CPP)
 
+option(ASSIMP_FAST_BUILD "build ASSIMP just for tests" ON)
+if(ASSIMP_FAST_BUILD)
+    option(ASSIMP_INSTALL FALSE)
+    option(ASSIMP_BUILD_ALL_IMPORTERS_BY_DEFAULT FALSE)
+    option(ASSIMP_BUILD_ALL_EXPORTERS_BY_DEFAULT FALSE)
+    foreach(FMT OBJ;PLY;STL;GLTF)
+        set(ASSIMP_BUILD_${FMT}_IMPORTER TRUE)
+        set(ASSIMP_BUILD_${FMT}_EXPORTER TRUE)
+    endforeach()
+endif()
+
 if(MSVC)
     set(MANIFOLD_FLAGS)
 else()