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/zlib/gz/gzclose.c

@@ -7,7 +7,6 @@
  */
 #include "third_party/zlib/gz/gzguts.inc"
 #include "third_party/zlib/macros.internal.h"
-// clang-format off
 
 /* gzclose() is in a separate file so that it is linked in only if it is used.
    That way the other gzclose functions can be used instead to avoid linking in

third_party/zlib/gz/gzguts.inc

@@ -4,7 +4,6 @@
 #include "third_party/zlib/macros.internal.h"
 #include "third_party/zlib/zlib.h"
 #include "third_party/zlib/zutil.internal.h"
-// clang-format off
 
 /* gzguts.h -- zlib internal header definitions for gz* operations
  * Copyright (C) 2004, 2005, 2010, 2011, 2012, 2013, 2016 Mark Adler

third_party/zlib/gz/gzlib.c

@@ -14,7 +14,6 @@
 #include "third_party/zlib/gz/gzguts.inc"
 #include "third_party/zlib/zlib.h"
 #include "third_party/zlib/zutil.internal.h"
-// clang-format off
 
 #define LSEEK lseek
 

third_party/zlib/gz/gzread.c

@@ -12,7 +12,6 @@
 #include "libc/str/str.h"
 #include "third_party/zlib/gz/gzguts.inc"
 #include "third_party/zlib/zlib.h"
-// clang-format off
 
 /* Local functions */
 local int gz_load OF((gz_statep, unsigned char *, unsigned, unsigned *));

third_party/zlib/gz/gzwrite.c

@@ -9,7 +9,6 @@
 #include "libc/mem/mem.h"
 #include "libc/stdio/stdio.h"
 #include "third_party/zlib/gz/gzguts.inc"
-// clang-format off
 
 /* Local functions */
 local int gz_init OF((gz_statep));