xuning / sherpaonnx

* Use PROJECT_SOURCE_DIR rather than CMAKE_SOURCE_DIR to allow building as subdirectory

* Also use PROJECT_SOURCE_DIR instead of CMAKE_SOURCE_DIR in c/cxx api examples

* Only build examples by default when not building as subdirectory

* Do not suggest building binaries either

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Co-authored-by: user <user@mail.tld>

v should be V

…ng directory for CMake (#2033)

We also need to clear _last