core: Fixed build constraints

Multiple constraints on the same line are combined with logical OR,
while combining multiple negated constraints needs to be done with
logical AND (each constraint on a separate line).

core/fmt/fmt_os.odin

@@ -1,4 +1,5 @@
-//+build !freestanding !js
+//+build !freestanding
+//+build !js
 package fmt
 
 import "core:runtime"

core/runtime/os_specific_any.odin

@@ -1,4 +1,8 @@
-//+build !freestanding !wasi !windows !js !darwin
+//+build !darwin
+//+build !freestanding
+//+build !js
+//+build !wasi
+//+build !windows
 package runtime
 
 import "core:os"