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>

plugins/meson.build

@@ -1,3 +1,7 @@
+if not get_option('plugins')
+  subdir_done()
+endif
+
 # Modules need more symbols than just those in plugins/qemu-plugins.symbols
 if not enable_modules
   if host_os == 'darwin'
@@ -12,29 +16,27 @@ if not enable_modules
   endif
 endif
 
-if get_option('plugins')
-  if host_os == 'windows'
-    dlltool = find_program('dlltool', required: true)
+if host_os == 'windows'
+  dlltool = find_program('dlltool', required: true)
 
-    # Generate a .lib file for plugins to link against.
-    # First, create a .def file listing all the symbols a plugin should expect to have
-    # available in qemu
-    win32_plugin_def = configure_file(
-      input: files('qemu-plugins.symbols'),
-      output: 'qemu_plugin_api.def',
-      capture: true,
-      command: ['sed', '-e', '0,/^/s//EXPORTS/; s/[{};]//g', '@INPUT@'])
-    # then use dlltool to assemble a delaylib.
-    win32_qemu_plugin_api_lib = configure_file(
-      input: win32_plugin_def,
-      output: 'libqemu_plugin_api.a',
-      command: [dlltool, '--input-def', '@INPUT@',
-                '--output-delaylib', '@OUTPUT@', '--dllname', 'qemu.exe']
-    )
-  endif
-  specific_ss.add(files(
-    'loader.c',
-    'core.c',
-    'api.c',
-  ))
+  # Generate a .lib file for plugins to link against.
+  # First, create a .def file listing all the symbols a plugin should expect to have
+  # available in qemu
+  win32_plugin_def = configure_file(
+    input: files('qemu-plugins.symbols'),
+    output: 'qemu_plugin_api.def',
+    capture: true,
+    command: ['sed', '-e', '0,/^/s//EXPORTS/; s/[{};]//g', '@INPUT@'])
+  # then use dlltool to assemble a delaylib.
+  win32_qemu_plugin_api_lib = configure_file(
+    input: win32_plugin_def,
+    output: 'libqemu_plugin_api.a',
+    command: [dlltool, '--input-def', '@INPUT@',
+              '--output-delaylib', '@OUTPUT@', '--dllname', 'qemu.exe']
+  )
 endif
+specific_ss.add(files(
+  'loader.c',
+  'core.c',
+  'api.c',
+))