os: add getuid and geteuid (#10002)

vlib/builtin/cfns.c.v

@@ -75,6 +75,10 @@ fn C.pclose(stream &C.FILE) int
 [trusted]
 fn C.getpid() int
 
+fn C.getuid() int
+
+fn C.geteuid() int
+
 fn C.system(cmd &char) int
 
 fn C.posix_spawn(child_pid &int, path &char, file_actions voidptr, attrp voidptr, argv &&char, envp &&char) int

vlib/os/os_nix.c.v

@@ -332,6 +332,16 @@ pub fn getpid() int {
 	return C.getpid()
 }
 
+[inline]
+pub fn getuid() int {
+	return C.getuid()
+}
+
+[inline]
+pub fn geteuid() int {
+	return C.geteuid()
+}
+
 // Turns the given bit on or off, depending on the `enable` parameter
 pub fn posix_set_permission_bit(path_s string, mode u32, enable bool) {
 	mut s := C.stat{}