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/fmodl.c

@@ -27,6 +27,7 @@
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/math.h"
 #include "libc/tinymath/ldshape.internal.h"
+#if !(LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024)
 
 asm(".ident\t\"\\n\\n\
 Musl libc (MIT License)\\n\
@@ -34,10 +35,13 @@ Copyright 2005-2014 Rich Felker, et. al.\"");
 asm(".include \"libc/disclaimer.inc\"");
 // clang-format off
 
+/**
+ * Does (𝑥 rem 𝑦) w/ round()-style rounding.
+ * @return remainder ∈ (-|𝑦|,|𝑦|) in %xmm0
+ * @define 𝑥-trunc(𝑥/𝑦)*𝑦
+ */
 long double fmodl(long double x, long double y) {
-#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
-	return fmod(x, y);
-#elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
+#if (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
 	union ldshape ux = {x}, uy = {y};
 	int ex = ux.i.se & 0x7fff;
 	int ey = uy.i.se & 0x7fff;
@@ -135,3 +139,5 @@ long double fmodl(long double x, long double y) {
 #error "architecture unsupported"
 #endif
 }
+
+#endif /* long double is long */