Fix warnings around load_shaders

src/doomdef.h

@@ -620,7 +620,7 @@ extern const char *compdate, *comptime, *comprevision, *compbranch;
 ///      	SRB2CB itself ported this from PrBoom+
 #define NEWCLIP
 
-/// Hardware renderer: OpenGL
+/// OpenGL shaders
 #define GL_SHADERS
 
 /// Handle touching sector specials in P_PlayerAfterThink instead of P_PlayerThink.

src/hardware/r_opengl/r_opengl.c

@@ -1871,8 +1871,13 @@ static void load_shaders(FSurfaceInfo *Surface, GLRGBAFloat *poly, GLRGBAFloat *
 			pglUseProgram(0);
 	}
 	else
-#endif
 		pglUseProgram(0);
+#else
+	(void)Surface;
+	(void)poly;
+	(void)tint;
+	(void)fade;
+#endif
 }
 
 // -----------------+