 - drop hardcoded -O3

Index: CMakeLists.txt
--- CMakeLists.txt.orig
+++ CMakeLists.txt
@@ -45,10 +45,6 @@ if(MSVC)
   endif()
 else()
   add_compile_options(-Wall)
-
-  if(NOT CMAKE_BUILD_TYPE MATCHES Debug)
-    add_compile_options(-O3)
-  endif()
 endif()
 
 get_directory_property(hasParent PARENT_DIRECTORY)
