meson: Expose library build type as global variables

Given that it can be computed using an error-prone strings comparisons it
is better to provide a variable everywhere, so that we don't have the
risk of comparing values that are always false.

gio/tests/gdbus-object-manager-example/meson.build

@@ -39,7 +39,7 @@ gdbus_example_objectmanager_rst_gen = custom_target('objectmanager-rst-gen',
 )
 
 extra_c_args = []
-if get_option('default_library') == 'static'
+if glib_build_static_only
   extra_c_args = '-DGDBUS_OBJECT_MANAGER_EXAMPLE_STATIC_COMPILATION'
 endif
 

gio/tests/meson.build

@@ -223,7 +223,7 @@ if host_machine.system() != 'windows'
   }
 
   # LD_PRELOAD modules don't work so well with AddressSanitizer
-  if have_rtld_next and get_option('default_library') != 'static' and get_option('b_sanitize') == 'none'
+  if have_rtld_next and glib_build_shared and get_option('b_sanitize') == 'none'
     gio_tests += {
       'gsocketclient-slow' : {
         'depends' : [
@@ -652,7 +652,7 @@ if meson.can_run_host_binaries()
 
   compiler_type = '--compiler=@0@'.format(cc.get_id())
 
-  if get_option('default_library') != 'static'
+  if glib_build_shared
     plugin_resources_c = custom_target('plugin-resources.c',
       input : 'test4.gresource.xml',
       output : 'plugin-resources.c',
@@ -983,6 +983,6 @@ endif
 
 subdir('services')
 
-if get_option('default_library') != 'static'
+if glib_build_shared
   subdir('modules')
 endif