flua: don't allow dlopen, et al., for bootstrap flua

There are some logistics issues that need to be sorted out here before we
can actually allow this to work.

It's not really safe to allow LUA_USE_DLOPEN with host lib paths being used.
The host system could have an entirely different lua version and this could
cause us to crash and burn.

If we want to revive this later, we need to make sure to define c module
paths inside OBJDIR that are compiled against whatever version we've
bootstrapped.

(cherry picked from commit c2a2b4f3cf11e770892a524df637f671f5989719)
(cherry picked from commit 967fbfd9e2b7a015d5cba1491badcdf9044b28b9)