Units(Meson): add a case for extracting alias_target as a run target

Signed-off-by: Masatake YAMATO <yamato@redhat.com>

Units/parser-meson.r/simple-meson.d/expected.tags

@@ -31,3 +31,7 @@ bench-message	input-5.meson	/^bench_message = executable('bench-message', source
 suites	input-5.meson	/^suites = [$/;"	variable
 Connection	input-5.meson	/^        benchmark('Connection', bench_connect, timeout: 60, kwargs: suite)$/;"	benchmark
 Message passing	input-5.meson	/^        benchmark('Message passing', bench_message, timeout: 120, kwargs: suite)$/;"	benchmark
+gi_docgen	input-6.meson	/^gi_docgen = find_program('gi-docgen')$/;"	variable
+gck	input-6.meson	/^subdir('gck')$/;"	subdir
+gcr	input-6.meson	/^subdir('gcr')$/;"	subdir
+docs	input-6.meson	/^alias_target('docs',$/;"	run

Units/parser-meson.r/simple-meson.d/input-6.meson

@@ -0,0 +1,13 @@
+# -*- Meson -*- 
+# Taken from docs/meson.build of gcr
+#
+gi_docgen = find_program('gi-docgen')
+
+subdir('gck')
+subdir('gcr')
+
+# Create a pseudo target that build all docs at once
+alias_target('docs',
+  gck_docs,
+  gcr_docs,
+)