Some .o files need to be rebuilt if config.h changes. Adding it to the
list of headers may still fail to solve the problem, because some of
the Makefiles use implicit rules or do not list dependencies properly.
When shell variables are unexpectedly empty, 'test' gets the wrong
number of arguments and becomes unhappy. Logical AND should not be
done with 'test EXPR1 -a EXPR2' in such cases, because 'test' logic
does not short-circuit. Replace with 'test EXPR1 && test EXPR2'.
Shell logic does short-circuit, and if the first test invocation
fails, the second will never occur, and will never encounter missing
arguments.
