* put most of the cross-compiling support into a function llvm_create_cross_target_internal.
* when CrossCompile is included it still generates a NATIVE target.
* llvm_create_cross_target function takes a target_name which should match a toolchain.
* llvm_create_cross_target can now be used to target more than one cross-compilation target.
llvm-svn: 232067
The basic idea is similar to the existing cross compilation support. A directory must be configured to build host versions of tablegen tools and llvm-config. This directory can be user provided (and configured), or it can be created during the build. During a build the native build directory will be configured and built to supply the tablegen tools used during the build. A user could also explicitly provide the tablegen executables to run on the CMake command line.
llvm-svn: 217105
