Make improvements

- Improve compatibility with Blink virtual machine
- Add non-POSIX APIs for joining threads and signal masks
- Never ever use anything except 32-bit integers for atomics
- Add some `#undef` statements to workaround `ctags` problems

libc/intrin/describedirfd.c

@@ -20,7 +20,11 @@
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/sysv/consts/at.h"
 
-const char *(DescribeDirfd)(char buf[12], int dirfd) {
+#ifdef DescribeDirfd
+#undef DescribeDirfd
+#endif
+
+const char *DescribeDirfd(char buf[12], int dirfd) {
   if (dirfd == AT_FDCWD) return "AT_FDCWD";
   FormatInt32(buf, dirfd);
   return buf;