[core/os] get_current_directory: Add allocator arg to targets where its missing

core/os/os_linux.odin

@@ -985,7 +985,7 @@ unset_env :: proc(key: string) -> Error {
 }
 
 @(require_results)
-get_current_directory :: proc() -> string {
+get_current_directory :: proc(allocator := context.allocator) -> string {
 	// NOTE(tetra): I would use PATH_MAX here, but I was not able to find
 	// an authoritative value for it across all systems.
 	// The largest value I could find was 4096, so might as well use the page size.