CMake build: Support building clang tooling without static libs

Create a FindClang.cmake and move all Clang configuration there.
Find Clang and choose static libraries if available, otherwise use
clang-cpp if available.
Add option to link to clang-cpp even if static libraries are available.

Fixes: QTCREATORBUG-23172
Change-Id: If40304d174469df0c786259e724cbee8de0e2d0e
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

CMakeLists.txt

@@ -43,12 +43,11 @@ find_package(Qt5
     QuickWidgets Sql Widgets Xml ${QT_TEST_COMPONENT}
   REQUIRED
 )
-
 find_package(Qt5 COMPONENTS LinguistTools)
+find_package(Qt5 COMPONENTS Designer DesignerComponents Help SerialPort Svg QUIET)
 
 find_package(Threads)
-
-find_package(Qt5 COMPONENTS Designer DesignerComponents Help SerialPort Svg QUIET)
+find_package(Clang QUIET)
 
 function (set_if_target var target)
    if (TARGET "${target}")
@@ -75,15 +74,6 @@ else()
 endif()
 install(TARGETS OptionalSvg EXPORT QtCreator)
 
-find_package(Clang COMPONENTS libclang QUIET)
-# silence a lot of warnings from building against llvm
-# this would better fit inside a central libclang detection/include cmake file, but since we do not
-# have one put it temporary here
-if(MSVC AND TARGET libclang)
-    target_compile_options(libclang INTERFACE /wd4100 /wd4141 /wd4146 /wd4244 /wd4267 /wd4291)
-endif()
-find_package(LLVM QUIET)
-
 if (APPLE)
   find_library(FWCoreFoundation CoreFoundation)
   find_library(FWCoreServices CoreServices)

cmake/FindClang.cmake

@@ -0,0 +1,14 @@
+find_package(Clang CONFIG)
+
+# silence a lot of warnings from building against llvm
+if(MSVC AND TARGET libclang)
+    target_compile_options(libclang INTERFACE /wd4100 /wd4141 /wd4146 /wd4244 /wd4267 /wd4291)
+endif()
+
+option(CLANGTOOLING_LINK_CLANG_DYLIB "Force linking of Clang tooling against clang-cpp" NO)
+
+if (TARGET clangTooling AND NOT CLANGTOOLING_LINK_CLANG_DYLIB)
+  set(CLANG_TOOLING_LIBS libclang clangTooling clangQuery clangIndex)
+elseif (TARGET clang-cpp)
+  set(CLANG_TOOLING_LIBS libclang clang-cpp)
+endif()

src/tools/clangpchmanagerbackend/CMakeLists.txt

@@ -3,7 +3,8 @@ add_subdirectory(source)
 add_qtc_executable(clangpchmanagerbackend
   DEPENDS
     clangrefactoringbackend_lib clangpchmanagerbackend_lib
-    clangTooling libclang Sqlite ClangSupport clangQuery clangIndex
+    Sqlite ClangSupport
+    ${CLANG_TOOLING_LIBS}
   SOURCES
     clangpchmanagerbackendmain.cpp
 )

src/tools/clangrefactoringbackend/source/CMakeLists.txt

@@ -1,10 +1,7 @@
 add_qtc_library(clangrefactoringbackend_lib STATIC
   PUBLIC_DEPENDS
     Threads::Threads
-    LLVMCore libclang
-    clangAST clangASTMatchers clangBasic clangDynamicASTMatchers clangFrontend
-    clangHandleCXX clangIndex clangLex
-    clangSerialization clangTooling clangQuery
+    ${CLANG_TOOLING_LIBS}
     ClangSupport
   PUBLIC_DEFINES CLANGSUPPORT_BUILD_LIB
   PUBLIC_INCLUDES