Do not adjust mtime timezone on Windows

PR win32/25302 notes that gdb will crash when trying to "run" even a
simple program on Windows.  The essential bug here is that the BFD
cache can easily be corrupted -- I have sent a separate patch for
that.

The particular reason that the cache is corrupted on Windows is that
gnulib overrides "stat" to make it do timezone adjustment -- but BFD
does not use this version of stat.  The difference here triggers the
latent cache bug, but can also cause other bugs as well; in particular
it can cause spurious warnings about source files being newer.

This patch simply removes the stat override on mingw, making gnulib
and BFD agree.

I tested this by backing out the local AdaCore changes to work around
this bug and then verifying that I could reproduce it.  Then, I
applied this patch and verified that "run" works again.

2020-09-08  Tom Tromey  <tromey@adacore.com>

	PR win32/25302:
	* update-gnulib.sh: Apply stat patch.
	* patches/0001-use-windows-stat: New file.
	* import/m4/stat.m4: Update.
	* configure: Rebuild.

gnulib/ChangeLog

@@ -1,3 +1,11 @@
+2020-09-08  Tom Tromey  <tromey@adacore.com>
+
+	PR win32/25302:
+	* update-gnulib.sh: Apply stat patch.
+	* patches/0001-use-windows-stat: New file.
+	* import/m4/stat.m4: Update.
+	* configure: Rebuild.
+
 2020-08-26  Christian Biesinger  <cbiesinger@google.com>
 	    Pedro Alves  <palves@redhat.com>
 	    Joel Brobecker  <brobecker@adacore.com>

gnulib/configure

@@ -26907,8 +26907,7 @@ $as_echo "#define ssize_t int" >>confdefs.h
 
   case "$host_os" in
     mingw*)
-                  REPLACE_STAT=1
-      ;;
+                        ;;
     *)
                         { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether stat handles trailing slashes on files" >&5
 $as_echo_n "checking whether stat handles trailing slashes on files... " >&6; }

gnulib/import/m4/stat.m4

@@ -15,7 +15,7 @@ AC_DEFUN([gl_FUNC_STAT],
     mingw*)
       dnl On this platform, the original stat() returns st_atime, st_mtime,
       dnl st_ctime values that are affected by the time zone.
-      REPLACE_STAT=1
+      dnl REPLACE_STAT=1
       ;;
     *)
       dnl AIX 7.1, Solaris 9, mingw64 mistakenly succeed on stat("file/").

gnulib/patches/0001-use-windows-stat

@@ -0,0 +1,13 @@
+diff --git a/gnulib/import/m4/stat.m4 b/gnulib/import/m4/stat.m4
+index 46e9abceee7..8ef355f9407 100644
+--- a/gnulib/import/m4/stat.m4
++++ b/gnulib/import/m4/stat.m4
+@@ -15,7 +15,7 @@ AC_DEFUN([gl_FUNC_STAT],
+     mingw*)
+       dnl On this platform, the original stat() returns st_atime, st_mtime,
+       dnl st_ctime values that are affected by the time zone.
+-      REPLACE_STAT=1
++      dnl REPLACE_STAT=1
+       ;;
+     *)
+       dnl AIX 7.1, Solaris 9, mingw64 mistakenly succeed on stat("file/").

gnulib/update-gnulib.sh

@@ -173,6 +173,8 @@ apply_patches ()
     fi
 }
 
+apply_patches "patches/0001-use-windows-stat"
+
 # Regenerate all necessary files...
 aclocal &&
 autoconf &&