Updated core lib and did cleanup

Updated core with some path related functions and did some minor code cleanup.
Most of the standard library function is just a matter of copy what is there for the other BSDs.

core/os/dir_bsd.odin

@@ -1,3 +1,4 @@
+//+build freebsd, netbsd
 package os
 
 import "core:mem"

core/os/os_netbsd.odin

@@ -483,6 +483,13 @@ is_dir_path :: proc(path: string, follow_links: bool = true) -> bool {
 is_file :: proc {is_file_path, is_file_handle}
 is_dir :: proc {is_dir_path, is_dir_handle}
 
+exists :: proc(path: string) -> bool {
+	runtime.DEFAULT_TEMP_ALLOCATOR_TEMP_GUARD()
+	cpath := strings.clone_to_cstring(path, context.temp_allocator)
+	res := _unix_access(cpath, O_RDONLY)
+	return res == 0
+}
+
 // NOTE(bill): Uses startup to initialize it
 
 stdin: Handle  = 0