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

test/libc/mem/critbit0_test.c

@@ -18,7 +18,6 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/mem/critbit0.h"
 #include "libc/fmt/itoa.h"
-#include "libc/intrin/bits.h"
 #include "libc/mem/critbit0.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/runtime.h"

test/libc/mem/malloc_test.c

@@ -22,7 +22,6 @@
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/asan.internal.h"
-#include "libc/intrin/bits.h"
 #include "libc/intrin/cxaatexit.internal.h"
 #include "libc/intrin/safemacros.internal.h"
 #include "libc/macros.internal.h"

test/libc/mem/qsort_test.c

@@ -16,7 +16,6 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/intrin/bits.h"
 #include "libc/macros.internal.h"
 #include "libc/mem/alg.h"
 #include "libc/mem/gc.h"

test/libc/mem/strdup_test.c

@@ -16,7 +16,6 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
-#include "libc/intrin/bits.h"
 #include "libc/mem/mem.h"
 #include "libc/testlib/testlib.h"