Have a single top-level main for running unit-tests

Instead of each .c file becoming a self-standing .t executable file,
and being run for executing the unit tests local to the file, now each
.c becomes a .to object (akin to a .o object, but one where the -DTEST
flag is given to the compiler).  After that, all the .to objects are
linked together in a gistatic-tests executable, in a equivalent way
that all .o files get linked together in a gistatic executable.

This change was necessary in order to allow dependencies between
objects.  The next task will be making a tar of a repository tree
checkout, and src/gistatic.{o,to} will start depending on
src/tar.{o,to}.  If each file has its own main function when -DTEST is
given, then I wont be able to link them together.

I took the opportunity that I had to change the Makefile, and I
improved the dependency between targets and dependencies greatly.  From
what I can tell now, it is correct.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/gistatic.h b/src/gistatic.h
index 03c02f6..7e022fa 100644
--- a/src/gistatic.h
+++ b/src/gistatic.h
@@ -3,4 +3,8 @@
 
 int gistatic_main(int argc, char *argv[]);
 
+#ifdef TEST
+void unit_tests_gistatic(void);
+#endif
+
 #endif