Preparatory work for allowing building of hannk with Emscripten; TFLite (and its dependees) problematic to build in that environment, but this will allow us to build a tflite-parser-only environment.

(Note that more work is needed to get this working for wasm, as crosscompiling in CMake is still pretty painful; this work was split out to make subsequent reviews simpler)

* Ignore local emsdk clone

* Fix usage of CMAKE_BUILD_TYPE

* Only print the Halide target info once per CMake run

* Fix Halide "cmake" target detection for Emscripten

* Prefer target_link_options to _link_libraries when applicable

* Validate, rather than find, NODE_JS_EXECUTABLE (set by emsdk)

* Emscripten already wraps tests with node.

* Add dependency on Android logging library.

* For cross-compiling, find host tools instead of recursive call.

Rather than shelling out via execute_process and potentially
guessing the toolchain options wrong, expect to find our host
tools (i.e. generators) in a package called "hannk_tools".

The package is created by the host build via the CMake export()
command. Importing this package in the cross build creates
IMPORTED targets with the same names as our generators. We then
use these generators rather than creating generators for the
target build.

* Rework cross-compiling script.

* Respond to (easy) reviewer comments.

* Add HANNK_AOT_HOST_ONLY option. Use in script.

* [hannk] tests should only process .tflite files (#6368)

currently, random dotfiles (e.g. .DS_Store on OSX) can creep in, causing bogus failures

* Add comment about node wrapping.

* Rename hannk_tools to hannk-halide_generators

* Add comment about exporting targets.

* Bump version to Halide 14.0.0 (#6369)

Co-authored-by: Steven Johnson <srj@google.com>