Toybox grep on a directory hits a uClibc bug and segfaults. This bug does not
happen in glibc, musl, or bionic, so it's not worth adding a workaround
upstream.

diff --git a/toys/posix/grep.c b/toys/posix/grep.c
index d44a92d..b9c2def 100644
--- a/toys/posix/grep.c
+++ b/toys/posix/grep.c
@@ -63,7 +63,8 @@ GLOBALS(
 // Show matches in one file
 static void do_grep(int fd, char *name)
 {
-  FILE *file = fdopen(fd, "r");
+  struct stat *st = (void *)(toybuf+sizeof(regex_t));
+  FILE *file = 0;
   long offset = 0;
   int lcount = 0, mcount = 0;
   char indelim = '\n' * !(toys.optflags&FLAG_z),
@@ -71,8 +72,13 @@ static void do_grep(int fd, char *name)
 
   if (!fd) name = "(standard input)";
 
+  if (!fstat(fd, st)) {
+    // grep * hits directories, skip but don't treat them as errors.
+    if (S_ISDIR(st->st_mode)) errno = 0;
+    else file = fdopen(fd, "r");
+  }
   if (!file) {
-    perror_msg("%s", name);
+    if (errno) perror_msg("%s", name);
     return;
   }