Mark functions printf-like where possible

These functions all take a format string and either a list of variable
arguments or a va_list. Use the new DRM_PRINTFLIKE macro to tell the
compiler about it so that the arguments can be checked against the
format string.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Thierry Reding <treding@nvidia.com>
diff --git a/xf86drm.c b/xf86drm.c
index 720952f..fa5701a 100644
--- a/xf86drm.c
+++ b/xf86drm.c
@@ -104,12 +104,16 @@
  * This function is a wrapper around vfprintf().
  */
 
-static int drmDebugPrint(const char *format, va_list ap)
+static int DRM_PRINTFLIKE(1, 0)
+drmDebugPrint(const char *format, va_list ap)
 {
     return vfprintf(stderr, format, ap);
 }
 
-static int (*drm_debug_print)(const char *format, va_list ap) = drmDebugPrint;
+typedef int DRM_PRINTFLIKE(1, 0) (*debug_msg_func_t)(const char *format,
+						     va_list ap);
+
+static debug_msg_func_t drm_debug_print = drmDebugPrint;
 
 void
 drmMsg(const char *format, ...)
@@ -129,7 +133,7 @@
 }
 
 void
-drmSetDebugMsgFunction(int (*debug_msg_ptr)(const char *format, va_list ap))
+drmSetDebugMsgFunction(debug_msg_func_t debug_msg_ptr)
 {
     drm_debug_print = debug_msg_ptr;
 }