build: Define glib_sanitizers variable to easily get the sanitizers in use

It's an array containing the list of sanitizers in use, normally it
contains a value, but in some cases may have more than one (e.g.
'address' and 'undefined').

And so use it to avoid repeated checks

gio/tests/meson.build

@@ -310,7 +310,7 @@ if host_machine.system() != 'windows'
   }
 
   # LD_PRELOAD modules don't work so well with AddressSanitizer
-  if have_rtld_next and glib_build_shared and get_option('b_sanitize') == 'none'
+  if have_rtld_next and glib_build_shared and glib_sanitizers.length() == 0
     gio_tests += {
       'gsocketclient-slow' : {
         'depends' : [

girepository/introspection/meson.build

@@ -9,7 +9,7 @@ gi_gen_shared_sources = [
 
 gi_gen_env_variables = environment()
 
-if get_option('b_sanitize') != 'none'
+if glib_sanitizers.length() > 0
   gi_gen_env_variables.append(
     'ASAN_OPTIONS', 'verify_asan_link_order=0', separator: ',')
 endif

meson.build

@@ -635,6 +635,11 @@ endif
 # improve this.
 glib_link_flags = cc.get_supported_link_arguments(warning_c_link_args)
 
+glib_sanitizers = get_option('b_sanitize').split(',')
+if glib_sanitizers == ['none']
+  glib_sanitizers = []
+endif
+
 # Windows SDK requirements and checks
 if host_system == 'windows'
   # Check whether we're building for UWP apps