Add extern "C" to all header files

mem/include/arena/mem_arena.h

@@ -4,6 +4,10 @@
 #include "aliases.h"
 #include <stdbool.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif // __cplusplus
+
 typedef struct growing_arena Arena;
 
 bool wapp_mem_arena_init(Arena **arena, u64 base_capacity);
@@ -12,4 +16,8 @@ void *wapp_mem_arena_alloc_aligned(Arena *arena, u64 size, u64 alignment);
 void wapp_mem_arena_clear(Arena *arena);
 void wapp_mem_arena_free(Arena **arena);
 
+#ifdef __cplusplus
+}
+#endif // __cplusplus
+
 #endif // !MEM_ARENA_H