run gnulib-tests in parallel

* tests/Makefile.am: Define AUTOMAKE_OPTIONS, so check.mk can append.
* tests/check.mk: Define SUFFIXES, so check.mk can append.
* build-aux/check.mk (SUFFIXES): Append, so as not to evoke
automake warning the prior definition in gnulib-tests/gnulib.mk.
(AUTOMAKE_OPTIONS): Likewise.
* gnulib-tests/Makefile.am (TEST_LOGS): Define.
Include build-aux/check.mk

build-aux/check.mk

@@ -41,7 +41,7 @@ ENABLE_HARD_ERRORS = :
 
 ## We use GNU Make extensions (%-rules) inside GNU_MAKE checks,
 ## and we override check-TESTS.
-AUTOMAKE_OPTIONS = -Wno-portability -Wno-override
+AUTOMAKE_OPTIONS += -Wno-portability -Wno-override
 
 # Restructured Text title and section.
 am__rst_title   = sed 's/.*/   &   /;h;s/./=/g;p;x;p;g;p;s/.*//'
@@ -145,7 +145,7 @@ echo "$$res: $@ (exit: $$estatus)" |			\
 cat $@-t >>$@;						\
 rm $@-t
 
-SUFFIXES = .html .log
+SUFFIXES += .html .log
 
 # From a test (with no extension) to a log file.
 if GNU_MAKE

gnulib-tests/Makefile.am

@@ -1 +1,6 @@
 include gnulib.mk
+
+TEST_LOGS = $(TESTS:=.log)
+
+# Parallel replacement of Automake's check-TESTS target.
+include $(top_srcdir)/build-aux/check.mk

tests/Makefile.am

@@ -564,4 +564,5 @@ pr_data =					\
   pr/ttb3-FF					\
   pr/w72l24f-ll
 
+AUTOMAKE_OPTIONS =
 include $(srcdir)/check.mk

tests/check.mk

@@ -91,6 +91,7 @@ TESTS_ENVIRONMENT =				\
 TEST_LOGS = $(TESTS:=.log)
 
 # Parallel replacement of Automake's check-TESTS target.
+SUFFIXES =
 include $(top_srcdir)/build-aux/check.mk
 
 VERBOSE = yes