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/proc/posix_spawn.c

@@ -37,6 +37,7 @@
 #include "libc/fmt/magnumstrs.internal.h"
 #include "libc/intrin/asan.internal.h"
 #include "libc/intrin/atomic.h"
+#include "libc/intrin/bsf.h"
 #include "libc/intrin/describeflags.internal.h"
 #include "libc/intrin/dll.h"
 #include "libc/intrin/strace.internal.h"
@@ -151,10 +152,11 @@ static textwindows bool spawnfds_exists(struct SpawnFds *fds, int fildes) {
   return fildes + 0u < fds->n && fds->p[fildes].kind;
 }
 
-static textwindows void spawnfds_close(struct SpawnFds *fds, int fildes) {
+static textwindows errno_t spawnfds_close(struct SpawnFds *fds, int fildes) {
   if (spawnfds_exists(fds, fildes)) {
     fds->p[fildes] = (struct Fd){0};
   }
+  return 0;
 }
 
 static textwindows errno_t spawnfds_dup2(struct SpawnFds *fds, int fildes,
@@ -181,8 +183,8 @@ static textwindows errno_t spawnfds_dup2(struct SpawnFds *fds, int fildes,
 }
 
 static textwindows errno_t spawnfds_open(struct SpawnFds *fds, int64_t dirhand,
-                                         int fildes, const char *path,
-                                         int oflag, int mode) {
+                                         const char *path, int oflag, int mode,
+                                         int fildes) {
   int64_t h;
   errno_t err;
   char16_t path16[PATH_MAX];
@@ -283,42 +285,47 @@ static textwindows errno_t posix_spawn_nt_impl(
   // apply user file actions
   if (file_actions) {
     for (struct _posix_faction *a = *file_actions; a && !err; a = a->next) {
+      char errno_buf[30];
+      char oflags_buf[128];
+      char openmode_buf[15];
+      (void)errno_buf;
+      (void)oflags_buf;
+      (void)openmode_buf;
       switch (a->action) {
         case _POSIX_SPAWN_CLOSE:
-          spawnfds_close(&fds, a->fildes);
+          err = spawnfds_close(&fds, a->fildes);
+          STRACE("spawnfds_close(%d) → %s", a->fildes,
+                 (DescribeErrno)(errno_buf, err));
           break;
         case _POSIX_SPAWN_DUP2:
           err = spawnfds_dup2(&fds, a->fildes, a->newfildes);
-          if (err) {
-            STRACE("spawnfds_dup2(%d, %d) failed", a->fildes, a->newfildes);
-            goto ReturnErr;
-          }
+          STRACE("spawnfds_dup2(%d, %d) → %s", a->fildes, a->newfildes,
+                 (DescribeErrno)(errno_buf, err));
           break;
         case _POSIX_SPAWN_OPEN:
-          err = spawnfds_open(&fds, dirhand, a->fildes, a->path, a->oflag,
-                              a->mode);
-          if (err) {
-            STRACE("spawnfds_open(%d, %#s) failed", a->fildes, a->path);
-            goto ReturnErr;
-          }
+          err = spawnfds_open(&fds, dirhand, a->path, a->oflag, a->mode,
+                              a->fildes);
+          STRACE("spawnfds_open(%#s, %s, %s, %d) → %s", a->path,
+                 (DescribeOpenFlags)(oflags_buf, a->oflag),
+                 (DescribeOpenMode)(openmode_buf, a->oflag, a->mode), a->fildes,
+                 (DescribeErrno)(errno_buf, err));
           break;
         case _POSIX_SPAWN_CHDIR:
           err = spawnfds_chdir(&fds, dirhand, a->path, &dirhand);
-          if (err) {
-            STRACE("spawnfds_chdir(%#s) failed", a->path);
-            goto ReturnErr;
-          }
+          STRACE("spawnfds_chdir(%#s) → %s", a->path,
+                 (DescribeErrno)(errno_buf, err));
           break;
         case _POSIX_SPAWN_FCHDIR:
           err = spawnfds_fchdir(&fds, a->fildes, &dirhand);
-          if (err) {
-            STRACE("spawnfds_fchdir(%d) failed", a->fildes);
-            goto ReturnErr;
-          }
+          STRACE("spawnfds_fchdir(%d) → %s", a->fildes,
+                 (DescribeErrno)(errno_buf, err));
           break;
         default:
           __builtin_unreachable();
       }
+      if (err) {
+        goto ReturnErr;
+      }
     }
   }
 
@@ -572,9 +579,13 @@ errno_t posix_spawn(int *pid, const char *path,
       }
     }
     if (flags & POSIX_SPAWN_SETRLIMIT) {
-      for (int rez = 0; rez <= ARRAYLEN((*attrp)->rlim); ++rez) {
-        if ((*attrp)->rlimset & (1u << rez)) {
-          if (setrlimit(rez, (*attrp)->rlim + rez)) {
+      int rlimset = (*attrp)->rlimset;
+      while (rlimset) {
+        int resource = _bsf(rlimset);
+        rlimset &= ~(1u << resource);
+        if (setrlimit(resource, (*attrp)->rlim + resource)) {
+          // MacOS ARM64 RLIMIT_STACK always returns EINVAL
+          if (!IsXnuSilicon()) {
             goto ChildFailed;
           }
         }