[Flang-RT] No flang hostdevice runtime flag

[DominikAdamski]

Merge only with: ROCm/llvm-project#756

Motivation

Modify aomp scripts to test PR: ROCm/llvm-project#328

Technical Details

This PR adds required changes to build GPU LLVM IR Flang runtime.

Test Plan

Test procedure:

1. Apply this PR
2. Apply LLVM PR: [Flang-RT] Changes required for embedded GPU LLVM IR Flang runtime llvm-project#328 for LLVM
3. Build AOMP :

./build_aomp.sh

a) (Optional) Build flang_rt.hostdevice if you want to use old -lflang_rt.hostdevice

./build_llvm-flang-rt-host-dev.sh

4. Test smoke-fort-dev for the new Flang RT:

IMPLICIT_GPU_FLANG_RT=1 ./check_smoke_fort_dev.sh 

(Optional) Test smoke-fort-dev for the old Flang RT (flang_rt.hostdevice):
Make sure, you built flang_rt.hostdevice (point 3a), and launch smoke_fort_dev tests (no additional env vars)

Test Result

No regression for smoke-fort-dev.