Typo bug in CMake from previous fix

Many commits here because I'm trying superbuild's update capabilities.

CMakeLists.txt

@@ -50,9 +50,7 @@ if (OJL_BIMAP_BUILD_TESTS)
     if (NOT CXX_20_SUPPORT)
         message(FATAL_ERROR "\
             The C++ compiler does not support the -std=c++20 flag\n\
-            Use a compiler that supports C++ 20, like clang++ >= 10\
-            ")
-        message(FATAL_ERROR 
+            Use a compiler that supports C++ 20, like clang++ >= 10")
     endif()