Make improvements

- You can now run `make -j8 toolchain` on Windows
- You can now run `make -j` on MacOS ARM64 and BSD OSes
- You can now use our Emacs dev environment on MacOS/Windows
- Fix bug where the x16 register was being corrupted by --ftrace
- The programs under build/bootstrap/ are updated as fat binaries
- The Makefile now explains how to download cosmocc-0.0.12 toolchain
- The build scripts under bin/ now support "cosmo" branded toolchains
- stat() now goes faster on Windows (shaves 100ms off `make` latency)
- Code cleanup and added review on the Windows signal checking code
- posix_spawnattr_setrlimit() now works around MacOS ARM64 bugs
- Landlock Make now favors posix_spawn() on non-Linux/OpenBSD
- posix_spawn() now has better --strace logging on Windows
- fstatat() can now avoid EACCES in more cases on Windows
- fchmod() can now change the readonly bit on Windows

libc/calls/fchmod-nt.c

@@ -0,0 +1,57 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/internal.h"
+#include "libc/calls/struct/fd.internal.h"
+#include "libc/calls/syscall-nt.internal.h"
+#include "libc/calls/syscall_support-nt.internal.h"
+#include "libc/nt/enum/fileflagandattributes.h"
+#include "libc/nt/enum/fileinfobyhandleclass.h"
+#include "libc/nt/files.h"
+#include "libc/nt/struct/filebasicinfo.h"
+#include "libc/sysv/errfuns.h"
+
+textwindows int sys_fchmod_nt(int fd, uint32_t mode) {
+
+  // validate file descriptor
+  if (fd + 0u >= g_fds.n) return ebadf();
+  if (g_fds.p[fd].kind == kFdEmpty) return ebadf();
+
+  // get current information
+  struct NtFileBasicInfo fbi;
+  if (!GetFileInformationByHandleEx(g_fds.p[fd].handle, kNtFileBasicInfo, &fbi,
+                                    sizeof(fbi))) {
+    return __winerr();
+  }
+
+  // change attributes
+  if (mode & 0222) {
+    fbi.FileAttributes &= ~kNtFileAttributeReadonly;
+  } else {
+    fbi.FileAttributes |= kNtFileAttributeReadonly;
+  }
+
+  // set new attributes
+  if (!SetFileInformationByHandle(g_fds.p[fd].handle, kNtFileBasicInfo, &fbi,
+                                  sizeof(fbi))) {
+    return __winerr();
+  }
+
+  // all good
+  return 0;
+}