Make fixes and improvements

- Polyfill UTIME_OMIT on XNU
- Refactor Lua build code so it's better
- Add unix module to lua.com (Discord request)
- Add unix.utimensat() and unix.futimens() to redbean
- Avoid creating double slash path in linenoise (#428)
- Remove double slashes in NT paths automatically (#428)
- Make strerror() smarter about showing NT errors (#428)

Fixes #428

libc/calls/mkntpath.c

@@ -80,10 +80,10 @@ textwindows int __mkntpath2(const char *path,
    * 5. Need ≥13 for mkdir() i.e. 1+8+3+1, e.g. "\\ffffffff.xxx\0"
    *    which is an "8.3 filename" from the DOS days
    */
-  char16_t *p;
   const char *q;
   bool isdospath;
-  size_t i, n, m, x, z;
+  char16_t c, *p;
+  size_t i, j, n, m, x, z;
   if (!path) return efault();
   path = FixNtMagicPath(path, flags);
   p = path16;
@@ -144,12 +144,20 @@ textwindows int __mkntpath2(const char *path,
     return enametoolong();
   }
 
-  // turn slash into backslash
-  for (i = 0; i < n; ++i) {
-    if (p[i] == '/') {
-      p[i] = '\\';
+  // 1. turn `/` into `\`
+  // 2. turn `\\` into `\` if not at beginning
+  for (j = i = 0; i < n; ++i) {
+    c = p[i];
+    if (c == '/') {
+      c = '\\';
     }
+    if (j > 1 && c == '\\' && p[j - 1] == '\\') {
+      continue;
+    }
+    p[j++] = c;
   }
+  p[j] = 0;
+  n = j;
 
   return x + m + n;
 }

libc/calls/utimensat-xnu.c

@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/internal.h"
+#include "libc/calls/struct/stat.h"
 #include "libc/nexgen32e/nexgen32e.h"
 #include "libc/sysv/consts/at.h"
 #include "libc/sysv/consts/utime.h"
@@ -26,21 +27,33 @@
 int sys_utimensat_xnu(int dirfd, const char *path, const struct timespec ts[2],
                       int flags) {
   int i;
+  struct stat st;
   struct timeval now, tv[2];
   if (flags) return einval();
   if (!ts || ts[0].tv_nsec == UTIME_NOW || ts[1].tv_nsec == UTIME_NOW) {
     gettimeofday(&now, NULL);
   }
+  if (ts && (ts[0].tv_nsec == UTIME_NOW || ts[1].tv_nsec == UTIME_NOW)) {
+    if (fstatat(dirfd, path, &st, flags) == -1) return -1;
+  }
   if (ts) {
-    for (i = 0; i < 2; ++i) {
-      if (ts[i].tv_nsec == UTIME_NOW) {
-        tv[i] = now;
-      } else if (ts[i].tv_nsec == UTIME_OMIT) {
-        return einval();
-      } else {
-        tv[i].tv_sec = ts[i].tv_sec;
-        tv[i].tv_usec = div1000int64(ts[i].tv_nsec);
-      }
+    if (ts[0].tv_nsec == UTIME_NOW) {
+      tv[0] = now;
+    } else if (ts[0].tv_nsec == UTIME_OMIT) {
+      tv[0].tv_sec = st.st_atim.tv_sec;
+      tv[0].tv_usec = div1000int64(st.st_atim.tv_nsec);
+    } else {
+      tv[0].tv_sec = ts[0].tv_sec;
+      tv[0].tv_usec = div1000int64(ts[0].tv_nsec);
+    }
+    if (ts[1].tv_nsec == UTIME_NOW) {
+      tv[1] = now;
+    } else if (ts[1].tv_nsec == UTIME_OMIT) {
+      tv[1].tv_sec = st.st_mtim.tv_sec;
+      tv[1].tv_usec = div1000int64(st.st_mtim.tv_nsec);
+    } else {
+      tv[1].tv_sec = ts[1].tv_sec;
+      tv[1].tv_usec = div1000int64(ts[1].tv_nsec);
     }
   } else {
     tv[0] = now;

libc/intrin/strerror_wr.greg.c

@@ -34,16 +34,18 @@
 privileged int strerror_wr(int err, uint32_t winerr, char *buf, size_t size) {
   /* kprintf() weakly depends on this function */
   int c, n;
+  bool wanting;
   char16_t winmsg[256];
   const char *sym, *msg;
-  sym = firstnonnull(strerrno(err), "EUNKNOWN");
-  msg = firstnonnull(strerdoc(err), "No error information");
+  wanting = false;
+  sym = firstnonnull(strerrno(err), (wanting = true, "EUNKNOWN"));
+  msg = firstnonnull(strerdoc(err), (wanting = true, "No error information"));
   if (IsTiny()) {
     if (!sym) sym = "EUNKNOWN";
     for (; (c = *sym++); --size)
       if (size > 1) *buf++ = c;
     if (size) *buf = 0;
-  } else if (!IsWindows() || err == winerr || !winerr) {
+  } else if (!IsWindows() || ((err == winerr || !winerr) && !wanting)) {
     ksnprintf(buf, size, "%s/%d/%s", sym, err, msg);
   } else {
     if ((n = FormatMessage(