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.

third_party/compiler_rt/fixxfti.c

@@ -12,6 +12,8 @@
  *
  * ===----------------------------------------------------------------------===
  */
+#include "libc/math.h"
+#if !(LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024)
 
 STATIC_YOINK("huge_compiler_rt_license");
 
@@ -52,3 +54,5 @@ __fixxfti(long double a)
 }
 
 #endif /* CRT_HAS_128BIT */
+
+#endif /* long double is long */