loci: chunk multiple classes into each C file

Parsing headers was taking more than half of the compile time for many classes.
By putting multiple classes into a single C file we amortize the cost of header
parsing. These C files are still much smaller than the old loci.c.

I also experimented with chunking the list and header class files, but there
are relatively few of these and so there was little gain.

The code size reduction is presumably due to better sharing of code between
similar classes. Since the classes are sorted by name before chunking the
action, instruction, etc inheritance hierarchies will be grouped together.

Results:
time make -j4 loci.a: -44% (27.4s to 15.4s)
strip loci.a && du -sh loci.a: -25% (2.3 MB to 1.7 MB)
Merge into master from pull request #210:
loci: chunk multiple classes into each C file (https://github.com/floodlight/loxigen/pull/210)