Merge #211: cmake: Fix hardening flags

e2f2f23 fixup! cmake: Add `HARDENING` option (Hennadii Stepanov)

Pull request description:

  During testing #93, a few issues were [noticed](#93 (comment)):
  - > `-mbranch-protection=bti` shouldn't be in C flags

  The other change simplifies the summary code in #93.

ACKs for top commit:
  m3dwards:
    ACK e2f2f23

Tree-SHA512: 386e3c180dbe68d76602bea12737651bbec398bfd5d75c32e3b235d418e60322e1c82ce08c4fb719e205705c5af2895d78d17d6907d8b370b5225dd8d4f0604b

CMakeLists.txt

@@ -504,7 +504,8 @@ if(ENABLE_HARDENING)
     try_append_linker_flag("/NXCOMPAT" TARGET hardening_interface)
   else()
     target_compile_options(hardening_interface INTERFACE
-      $<$<NOT:$<CONFIG:Debug>>:-U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3>
+      $<$<NOT:$<CONFIG:Debug>>:-U_FORTIFY_SOURCE>
+      $<$<NOT:$<CONFIG:Debug>>:-D_FORTIFY_SOURCE=3>
     )
 
     try_append_cxx_flags("-Wstack-protector" TARGET hardening_interface SKIP_LINK)
@@ -520,7 +521,7 @@ if(ENABLE_HARDENING)
     endif()
 
     if(CMAKE_SYSTEM_PROCESSOR STREQUAL "aarch64" OR CMAKE_SYSTEM_PROCESSOR STREQUAL "arm64")
-      try_append_cxx_flags("-mbranch-protection=bti" TARGET hardening_interface)
+      try_append_cxx_flags("-mbranch-protection=bti" TARGET hardening_interface SKIP_LINK)
     endif()
 
     try_append_linker_flag("-Wl,--enable-reloc-section" TARGET hardening_interface)