Use FORTIFY_SOURCE in release builds

gcc-14 warns when using FORTIFY_SOURCE in debug builds:

  /usr/include/features.h:414:4: warning: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Wcpp]
  414 | #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)
      |    ^~~~~~~

Use it in release builds instead.

CMakeLists.txt

@@ -49,7 +49,6 @@ endif()
 
 if(CMAKE_BUILD_TYPE STREQUAL "Release")
   add_compile_options("-march=native;-flto")
-elseif (CMAKE_BUILD_TYPE STREQUAL "Debug")
   add_compile_options("-D_FORTIFY_SOURCE=3")
 endif()