build refactor patches needed

[austinvhuang]

Follow-up to https://github.com/AnswerDotAI/gpu.cpp/pull/16 Few issues i'm running into so far:

• default target for make should be clang/make based and not require cmake
• cmake 3.28 is a bit high (on my system i have 3.25.1 installed) - what's the lowest we can get away with
• find argument usage isn't portable, on mac i get the error- find: -executable: unknown primary or operator
• I think the dollar dereferencing $$exepath might work different on mac, getting /bin/sh: xe_path: command not found errors.
• all examples should depend on dawnlib and run setup.py automatically if the shared library is not there
• there seem to be cross dependencies between examples, eg run_hello_world seems to be doing a find for matmul.

[austinvhuang]

Reverting for now with 60b1b7d5516c33eed765cdede27ac67a7fcc2c84 and 45e640d0be901ead33c91ddbc1b7d508fed81c32 the PR is staged in the dev branch for now.