Update 1996/schweikh3/Makefile for SunOS

Rather than make anyone manually update the Makefile (the command in the
README.md file suggested that one would use Makefile variables) or type
a more complicated command the Makefile now tries to compile the entry
as suggested if compilation fails. Thus one can type 'make all' and if
compilation fails it will try the SunOS way.

1996/schweikh3/README.md

@@ -33,14 +33,6 @@ But still it is a useful utility.  To use try:
 
 and thanks for the virtual memories!  :-)
 
-NOTE: On some systems such as SunOS, one may need to compile with:
-
-```make
-	${CC} ${CFLAGS} \
-	  -I. -D_POSIX_SOURCE '-Ddifftime(a,b)=(double)(b-a)' \
-	  schweikh3.c -o schweikh3
-```
-
 
 ## Author's remarks: