Fix PKCS11 module path search

Commit c5c1183 switched the loading
of the PKCS#11 module from dlopen() to krb5int_open_plugin().  Because
krb5int_open_plugin() includes a stat() test, this change has the
unintended consequence of requiring the module name to be an absolute
or relative path to the library, not a filename within the dynamic
linker search path.

Within krb5int_open_plugin(), only stat() the filename on the
platforms which will use the file type.

[ghudson@mit.edu: adjusted conditionals to call stat() on Windows;
rewrote commit message]

ticket: 9067 (new)
tags: pullup
target_version: 1.20-next

src/util/support/plugins.c

@@ -189,9 +189,10 @@ long KRB5_CALLCONV
 krb5int_open_plugin (const char *filepath, struct plugin_file_handle **h, struct errinfo *ep)
 {
     long err = 0;
-    struct stat statbuf;
     struct plugin_file_handle *htmp = NULL;
     int got_plugin = 0;
+#if defined(USE_CFBUNDLE) || defined(_WIN32)
+    struct stat statbuf;
 
     if (!err) {
         if (stat (filepath, &statbuf) < 0) {
@@ -201,18 +202,20 @@ krb5int_open_plugin (const char *filepath, struct plugin_file_handle **h, struct
                          filepath, strerror(err));
         }
     }
+#endif
 
     if (!err) {
         htmp = calloc (1, sizeof (*htmp)); /* calloc initializes ptrs to NULL */
         if (htmp == NULL) { err = ENOMEM; }
     }
 
 #if USE_DLOPEN
-    if (!err && ((statbuf.st_mode & S_IFMT) == S_IFREG
+    if (!err
 #if USE_CFBUNDLE
-                 || (statbuf.st_mode & S_IFMT) == S_IFDIR
+                 && ((statbuf.st_mode & S_IFMT) == S_IFREG
+                 || (statbuf.st_mode & S_IFMT) == S_IFDIR)
 #endif /* USE_CFBUNDLE */
-        )) {
+        ) {
         void *handle = NULL;
 
 #if USE_CFBUNDLE