buildsys: Fix building without plugins on Darwin

buildsys: Fix building without plugins on Darwin

Since commit 0082475e26 the plugin symbol list is unconditionally
added to the linker flags, leading to a build failure:

  Undefined symbols for architecture arm64:
    "_qemu_plugin_entry_code", referenced from:
        <initial-undefines>
  ...
  ld: symbol(s) not found for architecture arm64
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  ninja: build stopped: subcommand failed.

Fix by restricting the whole meson file to the --enable-plugins
configure argument.

Fixes: 0082475e26 ("meson: merge plugin_ldflags into emulator_link_args")
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2476
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20240813112457.92560-1-philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240813202329.1237572-9-alex.bennee@linaro.org>