[fullaot] configure.ac: pass --runtime=mobile to AOT_{BUILD,RUN}_FLAGS
For the profiles where we compile the BCL with -d:MOBILE, (where the
`[assembly: AssemblyVersion (Consts.FxVersion)]` attribute ends up pointing to
the mobile version) make sure we AOT and run the tests using the mobile
runtime. This ensures that for the framework assemblies the version number in
the assembly matches the version number that the internal runtime remapping (
`mono/metadata/assembly.c` `framework_assemblies` array)