Add note about strstr botch on sunos4.0.3c and previous.

gdb/config/sun3os4.mh

@@ -1,3 +1,5 @@
 # Host: Sun 3, running SunOS 4
+#msg If you are compiling on SunOS 4.0 through 4.0.3c, delete the line
+#msg in xm-sun3os4 that says `#define HAVE_STRSTR'.
 XDEPFILES= infptrace.o sun3-xdep.o
 XM_FILE= xm-sun3os4.h

gdb/config/sun4os4.mh

@@ -1,3 +1,5 @@
 # Host: Sun 4 or Sparcstation, running SunOS 4
+#msg If you are compiling on SunOS 4.0 through 4.0.3c, delete the line
+#msg in xm-sun4os4 that says `#define HAVE_STRSTR'.
 XDEPFILES= infptrace.o sparc-xdep.o
 XM_FILE= xm-sun4os4.h