Fix XNU / FreeBSD / OpenBSD / RHEL5 / NT bugs

For the first time ever, all tests in this codebase now pass, when
run automatically on macos, freebsd, openbsd, rhel5, rhel7, alpine
and windows via the network using the runit and runitd build tools

- Fix vfork exec path etc.
- Add XNU opendir() support
- Add OpenBSD opendir() support
- Add Linux history to syscalls.sh
- Use copy_file_range on FreeBSD 13+
- Fix system calls with 7+ arguments
- Fix Windows with greater than 16 FDs
- Fix RUNIT.COM and RUNITD.COM flakiness
- Fix OpenBSD munmap() when files are mapped
- Fix long double so it's actually long on Windows
- Fix OpenBSD truncate() and ftruncate() thunk typo
- Let Windows fcntl() be used on socket files descriptors
- Fix Windows fstat() which had an accidental printf statement
- Fix RHEL5 CLOCK_MONOTONIC by not aliasing to CLOCK_MONOTONIC_RAW

This is wonderful. I never could have dreamed it would be possible
to get it working so well on so many platforms with tiny binaries.

Fixes #31
Fixes #25
Fixes #14

libc/runtime/munmap.c

@@ -30,19 +30,20 @@
 /**
  * Releases memory pages.
  *
+ * This function may be used to punch holes in existing mappings, but your
+ * mileage may vary on Windows.
+ *
  * @param addr is a pointer within any memory mapped region the process
  *     has permission to control, such as address ranges returned by
  *     mmap(), the program image itself, etc.
- * @param size is the amount of memory to unmap, which needn't be a
- *     multiple of FRAMESIZE, and may be a subset of that which was
- *     mapped previously, and may punch holes in existing mappings,
- *     but your mileage may vary on windows
+ * @param size is the amount of memory to unmap, which needs to be a
+ *     multiple of FRAMESIZE for anonymous mappings, because windows
+ *     and for files size needs to be perfect to the byte bc openbsd
  * @return 0 on success, or -1 w/ errno
  */
 int munmap(void *addr, size_t size) {
   int rc;
   if (!ALIGNED(addr) || !CANONICAL(addr) || !size) return einval();
-  size = ROUNDUP(size, FRAMESIZE);
   if (UntrackMemoryIntervals(addr, size) == -1) return -1;
   if (IsWindows()) return 0;
   return munmap$sysv(addr, size);