Avoid automagic CXXFLAG detection courtesy of dev-libs/vc.

Gentoo-bug: 584118

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -525,10 +525,6 @@
     endif()
     endmacro()
 
-    if (NOT PACKAGERS_BUILD)
-        # Optimize everything for the current architecture
-        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${Vc_DEFINITIONS}")
-    endif ()
 endif()
 set(CMAKE_MODULE_PATH ${OLD_CMAKE_MODULE_PATH} )