and 3.4 to generate dependency files for the '.inc.h' files generated
from .td files, and .sinclude those dependency files in clang.build.mk.
This will make future incremental builds of lib/clang and usr.bin/clang
work correctly, whenever any of the .td files get modified.
Note that this will not fix any problems with incremental builds from
*before* this revision, since there will not yet be any generated
dependency files. A quick workaround is to run the following:
find /usr/obj -type f -name '*.inc.h' | xargs rm
and then a regular incremental buildworld (e.g. with -DNO_CLEAN).
MFC after: 3 days