[rocm-libraries] ROCm/rocm-libraries#7516 (commit de93737)

[CK] fix some jenkins logic errors. (#7516)

## Motivation

After merge from internal repo got some logic errors in the internal CI
jenkinsfile.
Here are 2 fixes for 2 issues:
1. make sure .ninja_log file exists before trying to parse it
2. use the default compiler for the gfx1250 target, since it's getting
built in its own special docker, which does not have the option of
installing alternative compilers.

## Technical Details

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## Test Plan

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## Test Result

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## Submission Checklist

- [ ] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.