[dataflow][patch] Convert conflict graph to lower triangular bit matrix

[Joern RENNECKE]

P.S.: Passing code as a macro argument is also a paradigm that we move
away from, since it causes trouble with sub-macros, preprocessor directives,
and line numbers of error messages/debug info.

Instead, we now use macros that expand to a partial statement, which is
completed by appending a block statement at the site where the macro is
used
.
For some examples, in the trunk/gcc directory, try:
grep FOR_EACH *.h