Splits out the few required dependencies to a FEXCore_Base static
library.
FEXCore then links to this directly.
Then make it so the FEX Common code links to FEXCore_Base so the
jemalloc dependency doesn't get pulled in.
Some distros include generated cmake files instead of the two cmake files from the source.
Distros that use the generated cmake files only have SDL import properties, so we are required
to use those.
Joshua Ashton