meson: Make private static library symbols local

Static libraries are not affected by our symbol file, so private symbols
are globally visible by default.

Use objcopy to make symbols that we do not want to expose local.

Closes: https://github.com/swaywm/wlroots/issues/1892
Closes: https://github.com/swaywm/wlroots/issues/2952

meson.build

@@ -150,8 +150,30 @@ lib_wlr = library(
 	install: true,
 	link_args: symbols_flag,
 	link_depends: symbols_file,
+	prelink: true,
 )
 
+if get_option('default_library') != 'shared'
+	lib_target = lib_wlr
+	if get_option('default_library') == 'both'
+		lib_target = lib_wlr.get_static_lib()
+	endif
+	objcopy_prog = find_program('objcopy', native: true)
+	custom_target('libwlroots',
+		input: lib_target,
+		output: lib_target.name() + '.is-stripped',
+		capture: true,
+		command: [
+			objcopy_prog.full_path(), '-w',
+			'--localize-symbol=!wlr_*',
+			'--localize-symbol=!_wlr_*',
+			'--localize-symbol=*',
+			'@INPUT@',
+		],
+		build_by_default: true,
+	)
+endif
+
 wlr_vars = {}
 foreach name, have : features
 	wlr_vars += { 'have_' + name.underscorify(): have.to_string() }