cmake: fix the LLVM linking logic ...

... when system contains both shared and static libraries and shared
libraries are preferred over the static one.
The current behavior is to link static libraries
even if shared ones are preferred.

`llvm_config` macro does the component to library resolution
automatically and will consider if any library contains more than one
components.

`ast` CMake target now uses the new style `target_link_libraries` to
match `llvm_config` macro's behavior to avoid CMake complaining that
mixing both styles is not allowed.

Author: liushuyu

src/ast/CMakeLists.txt

@@ -24,7 +24,7 @@ add_library(ast STATIC
 )
 
 target_compile_definitions(ast PRIVATE ${BPFTRACE_FLAGS})
-target_link_libraries(ast ast_defs arch parser)
+target_link_libraries(ast PUBLIC ast_defs arch parser)
 
 if(STATIC_LINKING)
   include(Util)
@@ -66,23 +66,19 @@ if(STATIC_LINKING)
   unlink_transitive_dependency("${CLANG_EXPORTED_TARGETS}" "$<LINK_ONLY:clang-cpp>")
 
   if(TARGET libclang_static)
-    target_link_libraries(ast libclang_static)
+    target_link_libraries(ast PUBLIC libclang_static)
   else()
     # old LLVM versions don't export libclang_static in ClangTargets.cmake; fall back to
     # libclang.a in that case
-    target_link_libraries(ast libclang.a)
+    target_link_libraries(ast PUBLIC libclang.a)
   endif()
 
-  target_link_libraries(ast ${clang_libs})
-  target_link_libraries(ast ${llvm_libs})
+  target_link_libraries(ast PUBLIC ${clang_libs})
+  target_link_libraries(ast PUBLIC ${llvm_libs})
 else()
-  find_library(found_LLVM LLVM HINTS ${LLVM_LIBRARY_DIRS})
-  if(found_LLVM)
-    target_link_libraries(ast LLVM)
-  else()
-    llvm_map_components_to_libnames(_llvm_libs bpfcodegen ipo irreader mcjit orcjit)
-    llvm_expand_dependencies(llvm_libs ${_llvm_libs})
-    target_link_libraries(ast ${llvm_libs})
-  endif()
-  target_link_libraries(ast libclang)
+  # llvm_config macro comes from the LLVM toolchain and will auto-resolve component
+  # names to library names. USE_SHARED option will tell llvm_config macro to prefer
+  # shared library / DLL on the system over the static libraries
+  llvm_config(ast USE_SHARED bpfcodegen ipo irreader mcjit orcjit)
+  target_link_libraries(ast PUBLIC libclang)
 endif()