Fix quotes in build.sh
    
    Earlier comment removed quotation from around command substitions $().
    This is not a good idea,
    because if the substitution produces whitespace,
    without the quotes, the result is not interpreted as a single string.
    Adding quotes back to places where they make sense.
    
    Apart from following good shell scripting practices,
    this commit fixes the problem where the script failed
    if the current working directory's patch contained whitespace.