Refactor some code

- Write tests for cthreads
- Fix bugs in pe2.com tool
- Fix ASAN issue with GetDosEnviron()
- Consolidate the cthread header files
- Some code size optimizations for MODE=
- Attempted to squash a tls linker warning
- Attempted to get futexes working on FreeBSD

libc/sysv/errno_location.greg.c

@@ -27,5 +27,5 @@
  */
 privileged nocallersavedregisters errno_t *(__errno_location)(void) {
   if (!__tls_enabled) return &__errno;
-  return (errno_t *)(__get_tls() + 0x3c);
+  return (errno_t *)(__get_tls_inline() + 0x3c);
 }