sim: move common flags to default AM_CPPFLAGS

sim: move common flags to default AM_CPPFLAGS

Since all host files we compile use these settings, move them out of
libcommon.a and into the default AM_CPPFLAGS.  This has the effect of
dropping the custom per-target automake rules.  Currently it saves us
~150 lines, but since it's about ~8 lines per object, the overhead
will increase quite a bit as we merge more files into a single build.

This also changes the object output names, so we have to tweak the
rules that were pulling in the common objects when linking.