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.

tool/scripts/cosmoc++

@@ -154,6 +154,10 @@ for x; do
   set -- "$@" "$x"
 done
 
+if [ x"$MODE" = x"nox87" ]; then
+  CCFLAGS="$CCFLAGS -mlong-double-64"
+fi
+
 if [ x"$OPT" != x"-Os" ] && [ x"${MODE#tiny}" != x"${MODE}" ]; then
   # support --ftrace unless optimizing for size
   CXXFLAGS="$CXXFLAGS -fpatchable-function-entry=18,16"

tool/scripts/cosmocc

@@ -154,6 +154,10 @@ for x; do
   set -- "$@" "$x"
 done
 
+if [ x"$MODE" = x"nox87" ]; then
+  CCFLAGS="$CCFLAGS -mlong-double-64"
+fi
+
 if [ x"$OPT" != x"-Os" ] && [ x"${MODE#tiny}" != x"${MODE}" ]; then
   # support --ftrace unless optimizing for size
   CFLAGS="$CFLAGS -fpatchable-function-entry=18,16"