[AMDGPU][Offload] Enable flang-rt build on amdhsa

Recent changes in CMake require to explicitly build the flang-rt for the
offload target.

Author: jplehr

buildbot/osuosl/master/config/builders.py

@@ -2122,7 +2122,7 @@ def collapseRequestsDoxygen(master, builder, req1, req2):
                             "-DCMAKE_CXX_STANDARD=17",
                             "-DBUILD_SHARED_LIBS=ON",
                             "-DLIBOMPTARGET_PLUGINS_TO_BUILD=amdgpu;host",
-                            "-DRUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES='compiler-rt;openmp'",
+                            "-DRUNTIMES_amdgcn-amd-amdhsa_LLVM_ENABLE_RUNTIMES='compiler-rt;openmp;flang-rt'",
                             "-DLLVM_RUNTIME_TARGETS=default;amdgcn-amd-amdhsa",
                             "-DCOMPILER_RT_BUILD_ORC=OFF",
                             "-DCOMPILER_RT_BUILD_XRAY=OFF",