## Exercise 10

 1. Write a script that builds a program from multiple sources.
 2. It takes a list of files as arguments (i.e. any number of
    arguments, one file name per argument).
 3. If the file is a ‹.c› or ‹.s›, compile it to an object.
 4. If the file is a ‹.o›, just keep it.
 5. Link all the ‹.o› files (including those compiled from sources)
    into a single executable (named ‹a.out›).
 6. If an argument does not exist or is not a ‹.c›, ‹.s› or a ‹.o›
    file, print an error and exit with a non-zero code.
 7. Make the script print the actions it takes, test it.
