Makefile: Use more effective compile flags

The ones added are pretty common, and useful.

  -O2 often gives a real performance boost.

  -g  gives us the needed debug symbols, and
      makes it much easier to blame the coder :)

N.B. -Wterror -Wextra -pedantic are (IMHO) of limited
     use, they just point to lesser errors, not the real
     ones.

Makefile

@@ -1,7 +1,7 @@
 #
 
 CFLAGS= -Wall -Werror -Wextra -pedantic \
-	-std=gnu99
+	-std=gnu99 -O2 -g
 
 LDFLAGS=-lm -lXaw -lXt -lX11
 # gcc -o xdu -O2 -fno-strength-reduce -fno-strict-aliasing      -L/usr/lib64   xdu.o xwin.o -lXaw -lXmu -lXt -lSM -lICE -lXpm  -lXext -lX11