Issue 39001: Breakpad Linux dumper: Refactor Makefile.
Issue 39001: Breakpad Linux dumper: Refactor Makefile.

Use GNU Make features to make the dumper, unit tests, and maintenance
targets more independent, so I get fewer conflicts as I work on
different parts of the patch series.

In particular:
- Provide targets to run tests and produce test coverage reports.
- Gather C and C++ build rules in one place.
- Avoid variables that list object files, as pattern rules can compute
  these values directly from the dependencies.
- Use VPATH to find sources in other directories.

a=jimb, r=nealsid


git-svn-id: 7939527bf0a06ad24ad020f729d5600cb42ed5d7@441 4c0a9323-5329-0410-9bdc-e9ce6186880e

AlekSi/google-breakpad-mirror,colesbury/google-breakpad,wincent/Google-Breakpad,albertz/google-breakpad,albertz/google-breakpad,mhoran/google-breakpad,Quiark/google-breakpad,wincent/Google-Breakpad,bbcallen/google-breakpad,bbcallen/google-breakpad,Quiark/google-breakpad,bbcallen/google-breakpad,bbcallen/google-breakpad,Quiark/google-breakpad,albertz/google-breakpad,AlekSi/google-breakpad-mirror,bittorrent/breakpad,bittorrent/breakpad,wesen/google-breakpad,wesen/google-breakpad,AlekSi/google-breakpad-mirror,AlekSi/google-breakpad-mirror,hkratz/breakpad_track_svn,colesbury/google-breakpad,colesbury/google-breakpad,mhoran/google-breakpad,mhoran/google-breakpad,hkratz/breakpad_track_svn,darwin/breakpad,wesen/google-breakpad,Quiark/google-breakpad,wesen/google-breakpad,Quiark/google-breakpad,hkratz/breakpad_track_svn,colesbury/google-breakpad,albertz/google-breakpad,wincent/Google-Breakpad,colesbury/google-breakpad,AlekSi/google-breakpad-mirror,wesen/google-breakpad,bittorrent/breakpad,bittorrent/breakpad,mhoran/google-breakpad,darwin/breakpad,bittorrent/breakpad,bbcallen/google-breakpad,bittorrent/breakpad,hkratz/breakpad_track_svn,bittorrent/breakpad,hkratz/breakpad_track_svn,colesbury/google-breakpad,albertz/google-breakpad,Quiark/google-breakpad,bbcallen/google-breakpad,mhoran/google-breakpad,wesen/google-breakpad,darwin/breakpad,mhoran/google-breakpad,albertz/google-breakpad,hkratz/breakpad_track_svn