system/coreutils: revert gnulib getcwd optimization. fixes #985, #987.

This commit reverts a commit in gnulib in coreutils that caused a
functional change between coreutils { 9.1 --> 9.2 }.

tl;dr:

  * on some systems, `(cd //tmp && /bin/pwd)` may return '/tmp' or
    '//tmp' depending on several factors; this is generally OK

  * in a musl-based Adélie environment, we identified a change in
    this behavior between coreutils updates during testing

  * the functional change was bisected to coreutils commit
    d42e4e9191abb818fc0e28507085a3945eed1477, which itself bumps
    the gnulib submodule, and is unrelated to coreutils itself

  * gnulib commit 356a414e8c15ef3f8cc7b7157427c8ce9a9f7c1b has been
    identified as the culprit for this functional change

See #987 for more information.

1 files changed, 92 insertions, 0 deletions

diff --git a/system/coreutils/revert-gnulib-getcwd-speedup-linux.patch b/system/coreutils/revert-gnulib-getcwd-speedup-linux.patch
new file mode 100644
index 000000000..fa8f66395
--- /dev/null
+++ b/system/coreutils/revert-gnulib-getcwd-speedup-linux.patch
@@ -0,0 +1,92 @@
+From d598f8169bbc9178c59d35f0df95637a70d3377f Mon Sep 17 00:00:00 2001
+From: Zach van Rijn <me@zv.io>
+Date: Mon, 10 Apr 2023 04:09:56 -0500
+Subject: [PATCH] Revert "getcwd: Speed up on Linux. Add support for Android."
+
+This reverts commit 356a414e8c15ef3f8cc7b7157427c8ce9a9f7c1b.
+
+diff --git a/lib/getcwd.c b/lib/getcwd.c
+index 0530630c43..04b8d2df39 100644
+--- a/lib/getcwd.c
++++ b/lib/getcwd.c
+@@ -173,9 +173,6 @@ __getcwd_generic (char *buf, size_t size)
+ #if HAVE_OPENAT_SUPPORT
+   int fd = AT_FDCWD;
+   bool fd_needs_closing = false;
+-# if defined __linux__
+-  bool proc_fs_not_mounted = false;
+-# endif
+ #else
+   char dots[DEEP_NESTING * sizeof ".." + BIG_FILE_NAME_COMPONENT_LENGTH + 1];
+   char *dotlist = dots;
+@@ -441,67 +438,6 @@ __getcwd_generic (char *buf, size_t size)
+ 
+       thisdev = dotdev;
+       thisino = dotino;
+-
+-#if HAVE_OPENAT_SUPPORT
+-      /* On some platforms, a system call returns the directory that FD points
+-         to.  This is useful if some of the ancestor directories of the
+-         directory are unreadable, because in this situation the loop that
+-         climbs up the ancestor hierarchy runs into an EACCES error.
+-         For example, in some Android app, /data/data/com.termux is readable,
+-         but /data/data and /data are not.  */
+-# if defined __linux__
+-      /* On Linux, in particular, if /proc is mounted,
+-           readlink ("/proc/self/fd/<fd>")
+-         returns the directory, if its length is < 4096.  (If the length is
+-         >= 4096, it fails with error ENAMETOOLONG, even if the buffer that we
+-         pass to the readlink function would be large enough.)  */
+-      if (!proc_fs_not_mounted)
+-        {
+-          char namebuf[14 + 10 + 1];
+-          sprintf (namebuf, "/proc/self/fd/%u", (unsigned int) fd);
+-          char linkbuf[4096];
+-          ssize_t linklen = readlink (namebuf, linkbuf, sizeof linkbuf);
+-          if (linklen < 0)
+-            {
+-              if (errno != ENAMETOOLONG)
+-                /* If this call was not successful, the next one will likely be
+-                   not successful either.  */
+-                proc_fs_not_mounted = true;
+-            }
+-          else
+-            {
+-              dirroom = dirp - dir;
+-              if (dirroom < linklen)
+-                {
+-                  if (size != 0)
+-                    {
+-                      __set_errno (ERANGE);
+-                      goto lose;
+-                    }
+-                  else
+-                    {
+-                      char *tmp;
+-                      size_t oldsize = allocated;
+-
+-                      allocated += linklen - dirroom;
+-                      if (allocated < oldsize
+-                          || ! (tmp = realloc (dir, allocated)))
+-                        goto memory_exhausted;
+-
+-                      /* Move current contents up to the end of the buffer.  */
+-                      dirp = memmove (tmp + dirroom + (allocated - oldsize),
+-                                      tmp + dirroom,
+-                                      oldsize - dirroom);
+-                      dir = tmp;
+-                    }
+-                }
+-              dirp -= linklen;
+-              memcpy (dirp, linkbuf, linklen);
+-              break;
+-            }
+-        }
+-# endif
+-#endif
+     }
+ 
+   if (dirstream && __closedir (dirstream) != 0)
+-- 
+2.25.1
+