Makefile.am: AM_TESTS_ENVIRONMENT -> LOG_COMPILER

    It’s important to note that, differently from what we’ve seen for
    the serial test harness (see Parallel Test Harness), the
    AM_TESTS_ENVIRONMENT and TESTS_ENVIRONMENT variables cannot be use
    to define a custom test runner; the LOG_COMPILER and LOG_FLAGS (or
    their extension-specific counterparts) should be used instead:

    ## This is WRONG!
    AM_TESTS_ENVIRONMENT = PERL5LIB='$(srcdir)/lib' $(PERL) -Mstrict -w

    ## Do this instead.
    AM_TESTS_ENVIRONMENT = PERL5LIB='$(srcdir)/lib'; export PERL5LIB;
    LOG_COMPILER = $(PERL)
    AM_LOG_FLAGS = -Mstrict -w

(http://www.gnu.org/software/automake/manual/html_node/Parallel-Test-Harness.html)

Makefile.am

@@ -92,7 +92,7 @@ protoc_c_protoc_c_LDADD = \
 # protobuf-c tests
 #
 
-AM_TESTS_ENVIRONMENT = $(VALGRIND)
+LOG_COMPILER = $(VALGRIND)
 
 check_PROGRAMS += \
 	t/generated-code/test-generated-code \