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.

test/libc/calls/pledge_test.c

@@ -32,7 +32,6 @@
 #include "libc/errno.h"
 #include "libc/intrin/kprintf.h"
 #include "libc/macros.internal.h"
-#include "libc/mem/copyfd.internal.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"

test/libc/calls/unveil_test.c

@@ -24,7 +24,6 @@
 #include "libc/dce.h"
 #include "libc/errno.h"
 #include "libc/intrin/kprintf.h"
-#include "libc/mem/copyfd.internal.h"
 #include "libc/mem/gc.h"
 #include "libc/runtime/internal.h"
 #include "libc/runtime/runtime.h"

test/libc/log/backtrace_test.c

@@ -26,7 +26,6 @@
 #include "libc/limits.h"
 #include "libc/log/libfatal.internal.h"
 #include "libc/log/log.h"
-#include "libc/mem/copyfd.internal.h"
 #include "libc/mem/gc.h"
 #include "libc/mem/mem.h"
 #include "libc/runtime/internal.h"

test/libc/stdio/system_test.c

@@ -18,7 +18,6 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
 #include "libc/dce.h"
-#include "libc/mem/copyfd.internal.h"
 #include "libc/mem/gc.h"
 #include "libc/paths.h"
 #include "libc/runtime/runtime.h"