Fix compiling with clang parser support and with Clang compiler, too (#7922)

* Fix compiling with clang parser support and with Clang compiler, too

When compiling the code with the Clang compiler a new CMake option
`use_libc++` is available which is enabled by default. It determines if
the Clang compiler should use libc++ as its C++ standard library or uses
the systems default (e.g. libstdc++ on Linux).
Disabling that option might help when compiling with Clang and the
option `use_libclang` is enabled but the associated library was not
built with libc++ as its C++ standard library.

Additionally, the doxygen executable that is created when CMake option
`static_libclang` is enabled, no longer crashes.

* Removing obsolete (and wrong) forcing of -std=c++11 for GCC

The entire Doxygen project already requires the compiler to run in C++14
mode. That setting is applied globally in the top-most `CMakeLists.txt`
file.
Therefore, forcing GCC to run in C++11 mode in `src/CMakeLists.txt` is
wrong and obsolete.

1 files changed, 8 insertions, 10 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 5ba80b7..8b11a2d 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -322,25 +322,23 @@ if (use_libclang)
         cmake_minimum_required(VERSION 3.1)
         target_compile_features(doxymain PRIVATE cxx_alignof)
         target_compile_features(doxygen PRIVATE cxx_alignof)
-        target_compile_options(doxymain PRIVATE -stdlib=libc++)
-        target_compile_options(doxygen PRIVATE -stdlib=libc++)
-    elseif (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-        target_compile_options(doxymain PRIVATE -std=c++11)
-        target_compile_options(doxygen PRIVATE -std=c++11)
+        if (use_libc++)
+            target_compile_options(doxymain PRIVATE -stdlib=libc++)
+            target_compile_options(doxygen PRIVATE -stdlib=libc++)
+        endif()
     endif()
     include_directories(${LLVM_INCLUDE_DIRS})
     add_definitions(${LLVM_DEFINITIONS})
     if (static_libclang)
-        llvm_map_components_to_libnames(llvm_libs support core option)
-        set(CLANG_LIBS libclang clangTooling ${llvm_libs})
+        set(CLANG_LIBS libclang clangTooling)
     else() # dynamically linked version of clang
-        llvm_map_components_to_libnames(llvm_libs support)
-        set(CLANG_LIBS libclang clang-cpp ${llvm_libs})
+        llvm_config(doxymain USE_SHARED support)
+        set(CLANG_LIBS libclang clang-cpp)
     endif()
     target_compile_definitions(doxygen PRIVATE ${LLVM_DEFINITIONS})
 endif()
 
-target_link_libraries(doxygen
+target_link_libraries(doxygen PRIVATE
     doxymain
     doxycfg
     qtools