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")
--- a/gstreamer-plugin/CMakeLists.txt
+++ b/gstreamer-plugin/CMakeLists.txt
@@ -30,8 +30,7 @@ set(flags_to_test
     -fstack-protector-strong
     -fPIE
     -fPIC
-    -flto
-    -D_FORTIFY_SOURCE=2)
+    -flto)
 if(NOT MSVC)
     list(INSERT flags_to_test 0 -Wall)
 else()
--- a/gstreamer-plugin/meson.build
+++ b/gstreamer-plugin/meson.build
@@ -20,7 +20,6 @@ svtav1enc_dep = dependency('SvtAv1Enc')
 cc = meson.get_compiler('c')
 cc_flags = [
     '-O2',
-    '-D_FORTIFY_SOURCE=2',
     '-Wformat',
     '-Wformat-security',
     '-fPIE',