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.

libc/x/xdtoal.c

@@ -20,6 +20,7 @@
 #include "libc/mem/mem.h"
 #include "libc/x/x.h"
 #include "third_party/gdtoa/gdtoa.h"
+#if !(LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024)
 
 /**
  * Converts long double to string the easy way.
@@ -31,9 +32,13 @@ char *xdtoal(long double d) {
 #if LDBL_MANT_DIG == 113
   p = xmalloc(64);
   g_Qfmt_p(p, &d, 16, 64, NIK(2, 0, 0));
-#else
+#elif LDBL_MANT_DIG == 64
   p = xmalloc(32);
   g_xfmt_p(p, &d, 16, 32, NIK(2, 0, 0));
+#else
+#error "unsupported long double"
 #endif
   return p;
 }
+
+#endif /* long double is long */