build: Use .m files directly

If we're on macOS we can count on an Objective C compiler to exist.

gio/Makefile.am

@@ -601,39 +601,17 @@ libgio_2_0_la_LDFLAGS = $(GLIB_LINK_FLAGS) \
 	-version-info $(LT_CURRENT):$(LT_REVISION):$(LT_AGE) \
 	-export-dynamic $(no_undefined)
 
-# We cannot build .m files because it would require adding AC_PROG_OBJC in
-# configure.ac, and it cannot be added conditionally. That means we would always
-# depend on an objective-c compiler even when not needed. To work around that
-# limitation we rename .m files to .c and compile them separately with
-# -xobjective-c into an intermediary library. Note that we cannot rename those
-# files to .c directly in the source tree because Meson needs the .m extension.
-# This must be done outside of "if OS_COCOA" block otherwise distcheck fails.
-# See https://bugzilla.gnome.org/show_bug.cgi?id=672777.
-OBJC_FILES = \
-	gnextstepsettingsbackend.m \
-	gosxcontenttype.m \
-	gosxappinfo.m \
-	gcocoanotificationbackend.m \
-	$(NULL)
-OBJC_C_FILES = $(OBJC_FILES:.m=.c)
-BUILT_SOURCES += $(OBJC_C_FILES)
-CLEANFILES += $(OBJC_C_FILES)
-EXTRA_DIST += $(OBJC_FILES)
-$(OBJC_C_FILES): %.c: %.m Makefile
-	cp $< $@
-
 if OS_COCOA
-libgio_objc_2_0_la_CFLAGS = $(libgio_2_0_la_CFLAGS) -xobjective-c
+libgio_objc_2_0_la_OBJCFLAGS = $(AM_OBJCFLAGS) $(libgio_2_0_la_CFLAGS)
 libgio_objc_2_0_la_CPPFLAGS = $(libgio_2_0_la_CPPFLAGS)
 libgio_objc_2_0_la_LDFLAGS = $(libgio_2_0_la_LDFLAGS) -Wl,-framework,Foundation -Wl,-framework,AppKit
 libgio_objc_2_0_la_SOURCES = \
-	gnextstepsettingsbackend.c \
+	gnextstepsettingsbackend.m \
-	gosxcontenttype.c \
+	gosxcontenttype.m \
-	gosxappinfo.c \
+	gosxappinfo.m
-	gosxappinfo.h
 if MAC_OS_X_9
 libgio_objc_2_0_la_SOURCES += \
-	gcocoanotificationbackend.c
+	gcocoanotificationbackend.m
 endif
 
 noinst_LTLIBRARIES += libgio-objc-2.0.la