[AIMIGRAPHX-828] Cross Compile Pt 2: add env variable to enable cross compilation

[kahmed10]

Motivation

builds on top of part 1: #4771

Technical Details

• adds environment variable MIGRAPHX_GPU_ARCH which can be set to whatever is supported by the compiler.
• when set, benchmarking kernels in compile_ops and finalize() will be disabled.
• will not work for MIOpen/hipblaslt/CK.

Changelog Category

Add a CHANGELOG.md entry for any option other than Not Applicable

• • Added: New functionality.
• • Changed: Changes to existing functionality.
• • Removed: Functionality or support that has been removed. (Compared to a previous release)
• • Optimized: Component performance that has been optimized or improved.
• • Resolved Issues: Known issues from a previous version that have been resolved.
• • Not Applicable: This PR is not to be included in the changelog.

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/program.cpp	60.00%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4795      +/-   ##
===========================================
- Coverage    92.49%   92.49%   -0.00%     
===========================================
  Files          583      583              
  Lines        29562    29565       +3     
===========================================
+ Hits         27343    27345       +2     
- Misses        2219     2220       +1     

Files with missing lines	Coverage Δ
src/include/migraphx/program.hpp	100.00% <ø> (ø)
src/program.cpp	72.00% <60.00%> (-0.02%)	⬇️

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