Fix eina file thread test on Windows

On windows, we try to open the "cmd.exe" file, but without the full path
the test fails unless it runs from the system directory.

We now use the full path to test the eina_file_open function.

Reviewed-by: Stefan Schmidt <stefan@datenfreihafen.org>
Reviewed-by: Vincent Torri <vincent.torri@gmail.com>
Reviewed-by: João Paulo Taylor Ienczak Zanette <joao.tiz@expertisesolutions.com.br>
Differential Revision: https://phab.enlightenment.org/D12021

src/tests/eina/eina_test_file.c

@@ -490,7 +490,29 @@ static void *
 _eina_test_file_thread(void *data EINA_UNUSED, Eina_Thread t EINA_UNUSED)
 {
 #ifdef _WIN32
-   const char *filename = "cmd.exe";
+   char filename[MAX_PATH];
+   size_t len;
+   const char test_file[] = "cmd.exe";
+
+   fail_if(!GetSystemDirectoryA(filename, MAX_PATH));
+
+   len = strlen(filename);
+
+   /*
+    * Check the buffer size.
+    * The system path length + path separator + length of the test_file + null terminator
+    * Must fit in MAX_PATH.
+    */
+   fail_if(MAX_PATH < len + 1 + sizeof(test_file));
+
+   // append trailing directory separator if there isn't one
+   if (filename[len - 1] != '\\' && filename[len - 1] != '/')
+     {
+         filename[len] = '\\';
+         filename[len + 1] = '\0';
+     }
+
+   strncat(filename, test_file, MAX_PATH - len - 2);
 #else
    const char *filename = "/bin/sh";
 #endif