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

libc/str/getzipcfileoffset.c

@@ -37,7 +37,7 @@ int64_t GetZipCfileOffset(const uint8_t *z) {
         offset += 8;
       }
       if (offset + 8 <= ZIP_EXTRA_CONTENTSIZE(p)) {
-        return READ64LE(ZIP_EXTRA_CONTENT(p) + offset);
+        return ZIP_READ64(ZIP_EXTRA_CONTENT(p) + offset);
       }
     }
   }