cmake: make clang-tidy optional if the tool is not found

[apwojcik]

The PR from the series to enable MIGraphX on Windows.

[pfultz2]

This should be done in rocm-cmake. Its fine to merge it into the UIF branch, but we wont merge it into develop.

[codecov]

Codecov Report

Merging #1895 (f34d72a) into develop (84a8f45) will not change coverage.
The diff coverage is n/a.

❗ Current head f34d72a differs from pull request most recent head 358ba8f. Consider uploading reports for the commit 358ba8f to get more accurate results

@@           Coverage Diff            @@
##           develop    #1895   +/-   ##
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  Coverage    91.44%   91.44%           
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  Files          419      419           
  Lines        15516    15516           
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  Hits         14188    14188           
  Misses        1328     1328           

[apwojcik]

merged to rocm-cmake