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/zstd/programs/benchfn.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/benchfn.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/benchzstd.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/benchzstd.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/datagen.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/datagen.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/dibio.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/dibio.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/fileio.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/fileio.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/fileio_asyncio.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/fileio_asyncio.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/fileio_common.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/fileio_types.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/platform.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/timefn.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/timefn.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/util.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/util.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/zstdcli.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/zstdcli_trace.c

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/zstdcli_trace.h

@@ -1,4 +1,3 @@
-// clang-format off
 /*
  * Copyright (c) Meta Platforms, Inc. and affiliates.
  * All rights reserved.

third_party/zstd/programs/zstdgrep

@@ -1,4 +1,3 @@
-// clang-format off
 #!/bin/sh
 #
 # Copyright (c) 2003 Thomas Klausner.