[Flang-RT] Changes required for embedded GPU LLVM IR Flang runtime

[DominikAdamski]

Motivation

Reduce linking time by embedding GPU LLVM IR code for Flang runtime.

Technical Details

Modified Flang runtime (added ifdefs to eliminate host-specific code from GPU compilation).

Test Plan

Checked smoke-fort-dev tests with new GPU Flang RT and the old flang_rt.hostdevice.

Test Result

I was able to compile and successfully run tests without flang_rt.hostdevice flag together with: ROCm/aomp#1755

[z1-cciauto]

PSDB Link: https://compiler-ci.amd.com/job/compiler-psdb-amd-staging/3092

[github-actions]

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