C23: add timespec_getres() and the new TIME_* constants.

Nothing to see here --- you'll want to keep using POSIX clock_gettime()
and clock_getres() instead. But portable code might use this eventually,
and it's trivial, so let's add it anyway.

(The whole "zero as an error return" precluding the direct use of
Linux's CLOCK_ constants is what really makes this a terrible API ---
we're going to have to add explicit translation any time they add a
new base.)

Test: treehugger
Change-Id: Iddb6cbe67b67b2b10fdd8b5ee654896d23deee47
diff --git a/libc/libc.map.txt b/libc/libc.map.txt
index c75b13a..0102b30 100644
--- a/libc/libc.map.txt
+++ b/libc/libc.map.txt
@@ -1584,6 +1584,11 @@
     posix_spawn_file_actions_addfchdir_np;
 } LIBC_T;
 
+LIBC_V { # introduced=VanillaIceCream
+  global:
+    timespec_getres;
+} LIBC_U;
+
 LIBC_PRIVATE {
   global:
     __accept4; # arm x86