[Cling] Disable warnings unknown to GCC or caused by LLVM

GCC does not understand the option -Wconditional-uninitialized,
and warns about some maybe uninitialized variables in LLVM.

core/clingutils/CMakeLists.txt

@@ -14,6 +14,11 @@ include_directories(${LLVM_INCLUDE_DIRS} ${CLING_INCLUDE_DIRS})
 include_directories(${CMAKE_CURRENT_SOURCE_DIR}/res ${CMAKE_CURRENT_SOURCE_DIR}/../foundation/res)
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${CLING_CXXFLAGS}")
 
+# This is to avoid warnings coming from GCC 7 in llvm/src/include/llvm/ADT/DenseMap.h:1010
+if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
+  ROOT_ADD_CXX_FLAG(CMAKE_CXX_FLAGS -Wno-maybe-uninitialized)
+endif()
+
 ROOT_OBJECT_LIBRARY(ClingUtils ${sources})
 
 add_dependencies(ClingUtils CLING)

core/metacling/CMakeLists.txt

@@ -19,9 +19,16 @@ else()
 set_source_files_properties(${CMAKE_CURRENT_SOURCE_DIR}/src/TClingCallbacks.cxx COMPILE_FLAGS -fno-rtti)
 endif()
 
-# This to avoid warning coming from  message coming from llvm/src/tools/clang/include/clang/Sema/Lookup.h:441
+# This to avoid warning coming from llvm/src/tools/clang/include/clang/Sema/Lookup.h:441
 # in clang + llvm version r227800.
-ROOT_ADD_CXX_FLAG(CMAKE_CXX_FLAGS -Wno-conditional-uninitialized)
+if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
+  ROOT_ADD_CXX_FLAG(CMAKE_CXX_FLAGS -Wno-conditional-uninitialized)
+endif()
+
+# This is to avoid warnings coming from GCC 7 in llvm/src/include/llvm/ADT/DenseMap.h:1010
+if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "GNU")
+  ROOT_ADD_CXX_FLAG(CMAKE_CXX_FLAGS -Wno-maybe-uninitialized)
+endif()
 
 ROOT_OBJECT_LIBRARY(MetaCling ${sources})
 add_dependencies(MetaCling CLING)