Merge branch '3rdparty_warn_fix' into 'develop'

Add compiler flag in 3rdparty cmake file to suppress warning on newer clang compilers

See merge request !40

Fit/3rdparty/RootMinimizers/CMakeLists.txt

@@ -16,11 +16,17 @@ file(GLOB source_files
 )
 
 add_definitions(-DWARNINGMSG)
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DMATH_NO_PLUGIN_MANAGER -DHAS_MINUIT2 -DR__HAS_MATHMORE")
+string(APPEND CMAKE_CXX_FLAGS " -DMATH_NO_PLUGIN_MANAGER -DHAS_MINUIT2 -DR__HAS_MATHMORE")
 if(NOT WIN32)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-deprecated-declarations")
+    string(APPEND CMAKE_CXX_FLAGS " -Wno-deprecated-declarations")
+    # suppresses a warning in
+    # Fit/3rdparty/RootMinimizers/mathcore/Math/GSLRngROOTWrapper.h
+    if(CMAKE_CXX_COMPILER_ID STREQUAL "Clang"
+        AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 10)
+      string(APPEND CMAKE_CXX_FLAGS " -Wno-dangling-gsl")
+    endif()
 else()
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /wd4244 /wd4267")
+    string(APPEND CMAKE_CXX_FLAGS " /wd4244 /wd4267")
 endif()
 
 add_library(${library_name} STATIC ${source_files})