configure: Allow passing extra Objective C compiler flags

We can pass C/CPP/LD flags via CFLAGS/CXXFLAGS/LDFLAGS environment
variables, or via configure --extra-cflags / --extra-cxxflags /
--extra-ldflags options. Provide similar behavior for Objective C:
use existing flags from $OBJCFLAGS, or passed via --extra-objcflags.

Reviewed-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Tested-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

configure

@@ -285,6 +285,7 @@ done
 
 EXTRA_CFLAGS=""
 EXTRA_CXXFLAGS=""
+EXTRA_OBJCFLAGS=""
 EXTRA_LDFLAGS=""
 
 xen_ctrl_version="$default_feature"
@@ -366,9 +367,12 @@ for opt do
   --extra-cflags=*)
     EXTRA_CFLAGS="$EXTRA_CFLAGS $optarg"
     EXTRA_CXXFLAGS="$EXTRA_CXXFLAGS $optarg"
+    EXTRA_OBJCFLAGS="$EXTRA_OBJCFLAGS $optarg"
     ;;
   --extra-cxxflags=*) EXTRA_CXXFLAGS="$EXTRA_CXXFLAGS $optarg"
   ;;
+  --extra-objcflags=*) EXTRA_OBJCFLAGS="$EXTRA_OBJCFLAGS $optarg"
+  ;;
   --extra-ldflags=*) EXTRA_LDFLAGS="$EXTRA_LDFLAGS $optarg"
   ;;
   --enable-debug-info) debug_info="yes"
@@ -748,6 +752,8 @@ for opt do
   ;;
   --extra-cxxflags=*)
   ;;
+  --extra-objcflags=*)
+  ;;
   --extra-ldflags=*)
   ;;
   --enable-debug-info)
@@ -1172,6 +1178,7 @@ Advanced options (experts only):
   --objcc=OBJCC            use Objective-C compiler OBJCC [$objcc]
   --extra-cflags=CFLAGS    append extra C compiler flags CFLAGS
   --extra-cxxflags=CXXFLAGS append extra C++ compiler flags CXXFLAGS
+  --extra-objcflags=OBJCFLAGS append extra Objective C compiler flags OBJCFLAGS
   --extra-ldflags=LDFLAGS  append extra linker flags LDFLAGS
   --cross-cc-ARCH=CC       use compiler when building ARCH guest test cases
   --cross-cc-cflags-ARCH=  use compiler flags when building ARCH guest tests
@@ -3137,6 +3144,7 @@ if test "$skip_meson" = no; then
   echo "[built-in options]" >> $cross
   echo "c_args = [$(meson_quote $CFLAGS $EXTRA_CFLAGS)]" >> $cross
   echo "cpp_args = [$(meson_quote $CXXFLAGS $EXTRA_CXXFLAGS)]" >> $cross
+  test -n "$objcc" && echo "objc_args = [$(meson_quote $OBJCFLAGS $EXTRA_OBJCFLAGS)]" >> $cross
   echo "c_link_args = [$(meson_quote $CFLAGS $LDFLAGS $EXTRA_CFLAGS $EXTRA_LDFLAGS)]" >> $cross
   echo "cpp_link_args = [$(meson_quote $CXXFLAGS $LDFLAGS $EXTRA_CXXFLAGS $EXTRA_LDFLAGS)]" >> $cross
   echo "[binaries]" >> $cross

meson.build

@@ -3467,6 +3467,11 @@ if link_language == 'cpp'
                                                + ['-O' + get_option('optimization')]
                                                + (get_option('debug') ? ['-g'] : []))}
 endif
+if targetos == 'darwin'
+  summary_info += {'OBJCFLAGS':       ' '.join(get_option('objc_args')
+                                               + ['-O' + get_option('optimization')]
+                                               + (get_option('debug') ? ['-g'] : []))}
+endif
 link_args = get_option(link_language + '_link_args')
 if link_args.length() > 0
   summary_info += {'LDFLAGS':         ' '.join(link_args)}