_build.sh: update cfguard related comment [ci skip]

Follow-up to 8afe58c
Follow-up to ca2c3ff
Follow-up to 80ccc39

Ref: #49

_build.sh

@@ -601,15 +601,20 @@ build_single_target() {
  fi
 
  if [ "${_TOOLCHAIN}" = 'llvm-mingw' ]; then
- # Requires llvm v16 and presumably mingw-w64 v11 with `--enable-cfguard`.
- # This is currently satified by llvm-mingw. The build also succeeds with
- # this combo without the `--enable-cfguard` option, with this warning:
- # ld.lld: warning: Control Flow Guard is enabled but '_load_config_used' is missing
+ # Requires llvm v16 and mingw-w64 v11 built with `--enable-cfguard`.
+ # As of 2023-08, this is satisfied by llvm-mingw only.
+ #
  # Refs:
  # https://github.com/mstorsjo/llvm-mingw/issues/301
  # https://gist.github.com/alvinhochun/a65e4177e2b34d551d7ecb02b55a4b0a
  # https://github.com/mstorsjo/llvm-mingw/compare/master...alvinhochun:llvm-mingw:alvin/cfguard.diff
  # https://github.com/mingw-w64/mingw-w64/compare/master...alvinhochun:mingw-w64:alvin/cfguard.diff
+ #
+ # The build is successful with standard distro llvm 16 + mingw-w64 11,
+ # but executables fail to run. The linker shows this warning:
+ # ld.lld: warning: Control Flow Guard is enabled but '_load_config_used' is missing
+ # By omitting the `-mguard=cf` linker option, the warning is gone, but
+ # the executables fail to run anyway.
  _CFLAGS_GLOBAL="${_CFLAGS_GLOBAL} -mguard=cf"
  _LDFLAGS_GLOBAL="${_LDFLAGS_GLOBAL} -mguard=cf"
  fi