[offload] Fix building standalone against LLVM dylib

When building standalone, and only LLVM dylib is installed, there are
no LLVM* library targets.  Skip the respective dependencies if
the targets are not present, and use the standard `llvm_config()`
function to link to the dylib, provided it supplies the needed library,
with a fallback to using the static library.

Note that I had to change PluginCommon into a STATIC library,
for compatibility with `llvm_config`.

Author: mgorny

offload/plugins-nextgen/amdgpu/CMakeLists.txt

@@ -8,14 +8,19 @@ target_sources(omptarget.rtl.amdgpu PRIVATE src/rtl.cpp)
 target_include_directories(omptarget.rtl.amdgpu PRIVATE
                            ${CMAKE_CURRENT_SOURCE_DIR}/utils)
 
+set(USE_SHARED)
+if (LLVM_LINK_LLVM_DYLIB)
+  set(USE_SHARED USE_SHARED)
+endif()
+llvm_config(omptarget.rtl.amdgpu ${USE_SHARED} FrontendOffloading)
+
 if(hsa-runtime64_FOUND AND NOT "amdgpu" IN_LIST LIBOMPTARGET_DLOPEN_PLUGINS)
   message(STATUS "Building AMDGPU plugin linked against libhsa")
-  target_link_libraries(omptarget.rtl.amdgpu PRIVATE hsa-runtime64::hsa-runtime64 LLVMFrontendOffloading)
+  target_link_libraries(omptarget.rtl.amdgpu PRIVATE hsa-runtime64::hsa-runtime64)
 else()
   message(STATUS "Building AMDGPU plugin for dlopened libhsa")
   target_include_directories(omptarget.rtl.amdgpu PRIVATE dynamic_hsa)
   target_sources(omptarget.rtl.amdgpu PRIVATE dynamic_hsa/hsa.cpp)
-  target_link_libraries(omptarget.rtl.amdgpu PRIVATE LLVMFrontendOffloading)
 endif()
 
 # Configure testing for the AMDGPU plugin. We will build tests if we could a

offload/plugins-nextgen/common/CMakeLists.txt

@@ -1,13 +1,16 @@
 # NOTE: Don't try to build `PluginInterface` using `add_llvm_library` because we
 # don't want to export `PluginInterface` while `add_llvm_library` requires that.
-add_library(PluginCommon OBJECT
+add_library(PluginCommon STATIC
   src/PluginInterface.cpp
   src/GlobalHandler.cpp
   src/JIT.cpp
   src/RPC.cpp
   src/Utils/ELF.cpp
 )
-add_dependencies(PluginCommon intrinsics_gen LLVMProfileData)
+add_dependencies(PluginCommon intrinsics_gen)
+if (TARGET LLVMProfileData)
+  add_dependencies(PluginCommon LLVMProfileData)
+endif()
 
 # Only enable JIT for those targets that LLVM can support.
 set(supported_jit_targets AMDGPU NVPTX)
@@ -43,7 +46,11 @@ target_compile_definitions(PluginCommon PRIVATE
 
 target_compile_options(PluginCommon PUBLIC ${offload_compile_flags})
 target_link_options(PluginCommon PUBLIC ${offload_link_flags})
-target_link_libraries(PluginCommon PRIVATE LLVMProfileData)
+set(USE_SHARED)
+if (LLVM_LINK_LLVM_DYLIB)
+  set(USE_SHARED USE_SHARED)
+endif()
+llvm_config(PluginCommon ${USE_SHARED} ProfileData)
 
 target_include_directories(PluginCommon PUBLIC
   ${CMAKE_CURRENT_SOURCE_DIR}/include