Merge remote-tracking branch 'model-validation/bugfix/fix-compile-ubuntu-20.04' into gh_179_180_182_183

Author: pcaspers

cmake/commonSettings.cmake

@@ -1,5 +1,7 @@
 include(CheckCXXCompilerFlag)
-include(CheckLinkerFlag)
+if(CMAKE_MINOR_VERSION GREATER 18 OR CMAKE_MINOR_VERSION EQUAL 18)
+    include(CheckLinkerFlag)
+endif()
 
 option(MSVC_LINK_DYNAMIC_RUNTIME "Link against dynamic runtime" ON)
 option(MSVC_PARALLELBUILD "Use flag /MP" ON)
@@ -145,7 +147,9 @@ else()
 
     # add pthread flag
     add_compiler_flag("-pthread" usePThreadCompilerFlag)
-    add_linker_flag("-pthread" usePThreadLinkerFlag)
+    if(CMAKE_MINOR_VERSION GREATER 18 OR CMAKE_MINOR_VERSION EQUAL 18)
+        add_linker_flag("-pthread" usePThreadLinkerFlag)
+    endif()
 
     if(QL_USE_PCH)
       # see https://ccache.dev/manual/4.8.3.html#_precompiled_headers