build: Set LC_ALL=C for check-local

This guarantees a reproducible environment for the test-suite.

Makecheck.am

@@ -15,6 +15,7 @@ check-clean:
 check-local: $(test_data) $(test_cases)
 	$(mkdir_p) $(test_tmpdir)
 	PATH="$(top_builddir)/src:$(top_builddir)/scripts:$(top_builddir)/utils:$(PATH)" \
+	  LC_ALL=C \
 	  $(TEST_ENV_VARS) \
 	  srcdir=$(srcdir) builddir=$(builddir) \
 	  PERL5LIB=$(top_srcdir)/scripts PERL_DL_NONLAZY=1 \