This makes sure that e.g. "make clean" actually removes
the built exe files, and avoids relinking the exe files each
time make is run when cross compiling from linux to windows.
(Make on windows seems to have an exception that knows to skip
rebuilding the 'h264enc' target if 'h264enc' doesn't exist but
'h264enc.exe' does, but this exception doesn't work on normal
unix make.)
Commit f38111d76b updated these files
manually (based on older versions of them) to something not generated
by the current mktargets.py/sh, losing the compact pattern rules.
This makes sure that all the dependency libs are built before trying
to link them together, fixing parallel make (which occasionally
failed due to trying to link the encoder or decoder command line
binaries before the libs had been built) and also fixes building an
individual component by e.g. "make h264enc".
