Just use stddef.h to get ptrdiff_t instead of obsolete malloc.h.
diff --git a/progs/tests/multipal.c b/progs/tests/multipal.c
index c824b38..fac652f 100644
--- a/progs/tests/multipal.c
+++ b/progs/tests/multipal.c
@@ -9,11 +9,7 @@
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
-#ifdef __VMS
-# include <stddef.h> /* for ptrdiff_t, referenced by GL.h when GL_GLEXT_LEGACY defined */
-#else
-# include <malloc.h> /* for ptrdiff_t, referenced by GL.h when GL_GLEXT_LEGACY defined */
-#endif
+#include <stddef.h> /* for ptrdiff_t, referenced by GL.h when GL_GLEXT_LEGACY defined */
#ifdef _WIN32
#include <windows.h>
#endif