configure.ac used AC_CANONICAL_SYSTEM to guess the GNU system
description triplets. The target description was substituted into the
Makefile and formatted into the filename for the binary distribution
tarball. But 'target' is only intended for cross-compilers. 'host_os'
might have been a better choice.
The tarball filename can still be changed manually, by running make with
an argument of 'DESTSYS=systemname'.
Cross-compiling may be more difficult now, but I am not certain that it
worked properly previously, and due to pending autoconf changes, it was
likely to break anyway.
The top-level config.guess and config.sub are no longer needed, but they
may reappear if better support for cross-compilation is added.
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.
