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/calls/clock_gettime.c

@@ -42,7 +42,6 @@
  * time. Among the more popular is CLOCK_MONOTONIC. This function has a
  * zero syscall implementation of that on modern x86.
  *
- *     nowl                l:        45𝑐        15𝑛𝑠
  *     rdtsc               l:        13𝑐         4𝑛𝑠
  *     gettimeofday        l:        44𝑐        14𝑛𝑠
  *     clock_gettime       l:        40𝑐        13𝑛𝑠