Use add_compiler_options to enable spectre mitigations and sdl checks (#6658)

CMakeLists.txt

@@ -41,8 +41,4 @@ if(CLR_CMAKE_HOST_WIN32)
         )
 endif(CLR_CMAKE_HOST_WIN32)
 
-if (MSVC)
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /Qspectre")
-endif()
-
 add_subdirectory(src/Profilers)

eng/native/override/configurecompiler.cmake

@@ -5,4 +5,7 @@ if (MSVC)
   add_linker_flag(/INCREMENTAL:NO DEBUG) # prevent "warning LNK4075: ignoring '/INCREMENTAL' due to '/OPT:REF' specification"
   add_linker_flag(/OPT:REF DEBUG)
   add_linker_flag(/OPT:NOICF DEBUG)
+
+  add_compile_options(/sdl)
+  add_compile_options(/Qspectre)
 endif(MSVC)