Replace system:System.framework imports with system:System

This makes the linker work for both macOS and iOS targets

core/sync/futex_darwin.odin

@@ -6,7 +6,7 @@ import "core:c"
 import "core:sys/darwin"
 import "core:time"
 
-foreign import System "system:System.framework"
+foreign import System "system:System"
 
 foreign System {
 	// __ulock_wait is not available on 10.15

core/sync/primitives_darwin.odin

@@ -5,7 +5,7 @@ package sync
 import "core:c"
 import "base:intrinsics"
 
-foreign import pthread "system:System.framework"
+foreign import pthread "system:System"
 
 _current_thread_id :: proc "contextless" () -> int {
 	tid: u64