main: Add MESA_VERBOSE=api support for glClearStencil

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/main/stencil.c

@@ -109,6 +109,9 @@ _mesa_ClearStencil( GLint s )
 {
    GET_CURRENT_CONTEXT(ctx);
 
+   if (MESA_VERBOSE & VERBOSE_API)
+      _mesa_debug(ctx, "glClearStencil(%d)\n", s);
+
    ctx->Stencil.Clear = (GLuint) s;
 }