update os layer

os_win32.cpp

@@ -0,0 +1,20 @@
+#ifndef OS_IMPL_WIN32_CPP
+#define OS_IMPL_WIN32_CPP
+
+#include "os.h"
+#include "Windows.h" 
+
+void *osAlloc(size_t capacity) {
+    return VirtualAlloc(NULL, sizeof(Arena) + capacity, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
+}
+
+void osReserve(void *ptr) {
+}
+
+void osDecommit(void *ptr) {
+}
+
+void osFree(void *ptr) {
+}
+
+#endif