Reduce header complexity

- Remove most __ASSEMBLER__ __LINKER__ ifdefs
- Rename libc/intrin/bits.h to libc/serialize.h
- Block pthread cancelation in fchmodat() polyfill
- Remove `clang-format off` statements in third_party

third_party/finger/display.c

@@ -42,7 +42,6 @@
 #include "libc/sysv/consts/fileno.h"
 #include "libc/sysv/consts/termios.h"
 #include "third_party/finger/finger.h"
-// clang-format off
 
 int
 getscreenwidth(void)

third_party/finger/finger.c

@@ -50,7 +50,6 @@
 #include "libc/time/time.h"
 #include "third_party/getopt/getopt.internal.h"
 #include "third_party/musl/passwd.h"
-// clang-format off
 
 /*
  * Mail status reporting added 931007 by Luke Mewburn, <zak@rmit.edu.au>.

third_party/finger/finger.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) 1989 The Regents of the University of California.
  * All rights reserved.

third_party/finger/lprint.c

@@ -43,7 +43,6 @@
 #include "libc/time/struct/tm.h"
 #include "libc/time/time.h"
 #include "third_party/finger/finger.h"
-// clang-format off
 
 /*
  * from: @(#)lprint.c	5.13 (Berkeley) 10/31/90

third_party/finger/net.c

@@ -42,7 +42,6 @@
 #include "libc/sysv/consts/af.h"
 #include "libc/sysv/consts/sock.h"
 #include "third_party/finger/finger.h"
-// clang-format off
 
 #ifndef lint
 /*static char sccsid[] = "from: @(#)net.c	5.5 (Berkeley) 6/1/90";*/

third_party/finger/sprint.c

@@ -40,7 +40,6 @@
 #include "libc/time/struct/tm.h"
 #include "libc/time/time.h"
 #include "third_party/finger/finger.h"
-// clang-format off
 
 #ifndef lint
 /*static char sccsid[] = "from: @(#)sprint.c	5.8 (Berkeley) 12/4/90";*/

third_party/finger/util.c

@@ -44,7 +44,6 @@
 #include "libc/str/str.h"
 #include "libc/sysv/consts/o.h"
 #include "third_party/finger/finger.h"
-// clang-format off
 
 #ifndef lint
 /*static char sccsid[] = "from: @(#)util.c	5.14 (Berkeley) 1/17/91";*/