Include objfiles.h in a few .c files

Include objfiles.h in a few .c files

I found a few .c files that rely on objfiles.h, but that only include
it indirectly, via dwarf2/read.h -> psympriv.h.  If that include is
removed (something my new DWARF indexer series does), then the build
will break.

It seemed harmless and correct to add these includes now, making the
eventual series a little smaller.