https://bugs.gentoo.org/890280

Don't override our toolchain defaults, which may be F_S=3 on some profiles, and
F_S=2 otherwise.
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -325,10 +325,6 @@ else()
     check_both_flags_add(-mno-avx)
 endif()
 
-if(CMAKE_C_FLAGS MATCHES "-O" AND NOT CMAKE_C_FLAGS MATCHES "-O0" AND NOT MINGW)
-    add_definitions(-D_FORTIFY_SOURCE=2)
-endif()
-
 if(CMAKE_ASM_NASM_OBJECT_FORMAT MATCHES "win")
     set(CMAKE_ASM_NASM_FLAGS_DEBUG "${CMAKE_ASM_NASM_FLAGS_DEBUG} -gcv8")
 elseif(CMAKE_ASM_NASM_COMPILER MATCHES "nasm")