ltmain.in: Add 'S_ISDIR' definition for MSVC

Several test failures occur from fix for sr #111191 with MSVC, which is
fixed by defining S_ISDIR with a different variable name, MSVC_ISDIR.

  error LNK2019: unresolved external symbol S_ISDIR referenced in func check_executable

* build-aux/ltmain.in: Define and use macro MSVC_ISDIR.

build-aux/ltmain.in

diff --git a/build-aux/ltmain.in b/build-aux/ltmain.in
index bc1457e..af01443 100644
--- a/build-aux/ltmain.in
+++ b/build-aux/ltmain.in
@@ -3859,6 +3859,7 @@
 # define getcwd  _getcwd
 # define putenv  _putenv
 # define S_IXUSR _S_IEXEC
+# define MSVC_ISDIR(m)(((m) & S_IFMT) == S_IFDIR)
 #elif defined __MINGW32__
 # define setmode _setmode
 # define stat    _stat
@@ -4254,8 +4255,13 @@
   if ((!path) || (!*path))
     return 0;
 
+#ifdef _MSC_VER
+  if ((stat (path, &st) >= 0) && !MSVC_ISDIR (st.st_mode)
+      && (st.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)))
+#else
   if ((stat (path, &st) >= 0) && !S_ISDIR (st.st_mode)
       && (st.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH)))
+#endif
     return 1;
   else
     return 0;