Make improvements

- More timspec_*() and timeval_*() APIs have been introduced.
- The copyfd() function is now simplified thanks to POSIX rules.
- More Cosmo-specific APIs have been moved behind the COSMO define.
- The setitimer() polyfill for Windows NT is now much higher quality.
- Fixed build error for MODE=aarch64 due to -mstringop-strategy=loop.
- This change introduces `make MODE=nox87 toolchain` which makes it
  possible to build programs using your cosmocc toolchain that don't
  have legacy fpu instructions. This is useful, for example, if you
  want to have a ~22kb tinier blink virtual machine.

tool/viz/printpeb.c

@@ -21,7 +21,6 @@
 #include "libc/dce.h"
 #include "libc/intrin/safemacros.internal.h"
 #include "libc/log/log.h"
-#include "libc/mem/copyfd.internal.h"
 #include "libc/nt/dll.h"
 #include "libc/nt/enum/filetype.h"
 #include "libc/nt/enum/startf.h"
@@ -58,7 +57,7 @@ int NextBestThing(void) {
   int64_t fd = open("/proc/self/maps", O_RDONLY);
   posix_fadvise(fd, 0, 0, MADV_SEQUENTIAL);
   ssize_t wrote;
-  while ((wrote = _copyfd(fd, 1, -1)) != -1) {
+  while ((wrote = copyfd(fd, 1, -1)) != -1) {
     if (wrote == 0) break;
   }
   close(fd);