Use CMake SET instead of string CONCAT

pjohnmeyer · pjohnmeyer · commit e161d4407764 · 2016-08-27T10:04:54.000-05:00
string(CONCAT...) was not available in older versions of CMake
targeted by this project.
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -33,7 +33,7 @@ if (${UTPP_AMPLIFY_WARNINGS})
     if(CMAKE_CXX_FLAGS MATCHES "/W[0-4]")
         string(REGEX REPLACE "/W[0-4]" "/W4" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /WX")
     else()
-        string(CONCAT CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}" " -Wall -Wextra -Werror -Wno-ignored-qualifiers")
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Wextra -Werror -Wno-ignored-qualifiers")
     endif()
 endif()
 
