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/tinymath/rempio2l.c

@@ -29,6 +29,7 @@
 #include "libc/math.h"
 #include "libc/tinymath/kernel.internal.h"
 #include "libc/tinymath/ldshape.internal.h"
+#if !(LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024)
 
 asm(".ident\t\"\\n\\n\
 FreeBSD libm (BSD-2 License)\\n\
@@ -200,3 +201,5 @@ int __rem_pio2l(long double x, long double *y)
 #else
 #error "architecture unsupported"
 #endif
+
+#endif /* long double is long */