The symbol file is a file that aids in debugging by allowing a crash
dump from a stripped executable to have it's symbols applied to it. The
file itself ends up in ./internal/temp after compilation and is called
`EXEFILE.sym`.
FIxes: #53
The Makefile was incorrectly tying together _ICON and icon.rc, making it
impossible to use one without the other. To fix this we introduce a new
DEP_ICON_RC flag, which indicates we need to use the icon.rc file (in
addition to regular icon support). DEP_ICON now only indicates we need
to support _ICON, and does not attempt to build the resource
information.