build: fix building on Windows due to _FORTIFY_SOURCE changes in MSYS2

Also, enable other hardening options that work on Windows with GCC 9.x

CMakeLists.txt

@@ -620,7 +620,7 @@ else()
   add_cxx_flag_if_supported(-Wformat-security CXX_SECURITY_FLAGS)
 
   # -fstack-protector
-  if (NOT WIN32 AND NOT OPENBSD)
+  if (NOT OPENBSD AND NOT (WIN32 AND (CMAKE_C_COMPILER_ID STREQUAL "GNU" AND CMAKE_C_COMPILER_VERSION VERSION_LESS 9.1)))
     add_c_flag_if_supported(-fstack-protector C_SECURITY_FLAGS)
     add_cxx_flag_if_supported(-fstack-protector CXX_SECURITY_FLAGS)
     add_c_flag_if_supported(-fstack-protector-strong C_SECURITY_FLAGS)
@@ -628,9 +628,11 @@ else()
   endif()
 
   # New in GCC 8.2
-  if (NOT WIN32 AND NOT OPENBSD)
+  if (NOT OPENBSD AND NOT (WIN32 AND (CMAKE_C_COMPILER_ID STREQUAL "GNU" AND CMAKE_C_COMPILER_VERSION VERSION_LESS 9.1)))
     add_c_flag_if_supported(-fcf-protection=full C_SECURITY_FLAGS)
     add_cxx_flag_if_supported(-fcf-protection=full CXX_SECURITY_FLAGS)
+  endif()
+  if (NOT WIN32 AND NOT OPENBSD)
     add_c_flag_if_supported(-fstack-clash-protection C_SECURITY_FLAGS)
     add_cxx_flag_if_supported(-fstack-clash-protection CXX_SECURITY_FLAGS)
   endif()
@@ -642,8 +644,8 @@ else()
   endif()
 
   # linker
-  if (NOT WIN32)
-    # Windows binaries die on startup with PIE
+  if (NOT (WIN32 AND (CMAKE_C_COMPILER_ID STREQUAL "GNU" AND CMAKE_C_COMPILER_VERSION VERSION_LESS 9.1)))
+    # Windows binaries die on startup with PIE when compiled with GCC <9.x
     add_linker_flag_if_supported(-pie LD_SECURITY_FLAGS)
   endif()
   add_linker_flag_if_supported(-Wl,-z,relro LD_SECURITY_FLAGS)