buildsys: Only display Objective-C information when Objective-C is used

When configuring with '--disable-cocoa --disable-coreaudio'
on Darwin, we get:

 meson.build:4081:58: ERROR: Tried to access compiler for language "objc", not specified for host machine.
 meson.build:4097:47: ERROR: Tried to access unknown option 'objc_args'.

Instead of unconditionally display Objective-C informations
on Darwin, display them when Objective-C is discovered.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20231009093812.52915-1-philmd@linaro.org>

meson.build

@@ -4087,8 +4087,10 @@ if 'cpp' in all_languages
 else
   summary_info += {'C++ compiler':      false}
 endif
-if targetos == 'darwin'
+if 'objc' in all_languages
   summary_info += {'Objective-C compiler': ' '.join(meson.get_compiler('objc').cmd_array())}
+else
+  summary_info += {'Objective-C compiler': false}
 endif
 option_cflags = (get_option('debug') ? ['-g'] : [])
 if get_option('optimization') != 'plain'
@@ -4098,7 +4100,7 @@ summary_info += {'CFLAGS':            ' '.join(get_option('c_args') + option_cfl
 if 'cpp' in all_languages
   summary_info += {'CXXFLAGS':        ' '.join(get_option('cpp_args') + option_cflags)}
 endif
-if targetos == 'darwin'
+if 'objc' in all_languages
   summary_info += {'OBJCFLAGS':       ' '.join(get_option('objc_args') + option_cflags)}
 endif
 link_args = get_option('c_link_args')