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/modfl.c

@@ -26,6 +26,7 @@
 │                                                                              │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/math.h"
+#if !(LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024)
 
 asm(".ident\t\"\\n\\n\
 Musl libc (MIT License)\\n\
@@ -33,20 +34,11 @@ Copyright 2005-2014 Rich Felker, et. al.\"");
 asm(".include \"libc/disclaimer.inc\"");
 // clang-format off
 
-#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
-long double modfl(long double x, long double *iptr)
-{
-	double d;
-	long double r;
-
-	r = modf(x, &d);
-	*iptr = d;
-	return r;
-}
-#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
-
 static const long double toint = 1/LDBL_EPSILON;
 
+/**
+ * Returns fractional part of 𝑥.
+ */
 long double modfl(long double x, long double *iptr)
 {
 	union {
@@ -90,6 +82,4 @@ long double modfl(long double x, long double *iptr)
 	return -y;
 }
 
-#else
-#error "architecture unsupported"
-#endif
+#endif /* long double is long */