tests: Use atlocal/atlocal.in to enable/disable the NAT test

Kill the hacking, use atlocal to remember if the NAT test should
be enabled and then skip the test (exit with 77).
diff --git a/openbsc/.gitignore b/openbsc/.gitignore
index 04ebc2f..a3ccd45 100644
--- a/openbsc/.gitignore
+++ b/openbsc/.gitignore
@@ -54,6 +54,7 @@
 tests/gprs/gprs_test
 
 tests/atconfig
+tests/atlocal
 tests/package.m4
 tests/testsuite
 tests/testsuite.log
diff --git a/openbsc/configure.ac b/openbsc/configure.ac
index 636416b..56e4b60 100644
--- a/openbsc/configure.ac
+++ b/openbsc/configure.ac
@@ -29,6 +29,7 @@
         osmo_ac_build_nat="no"
     ])
 AM_CONDITIONAL(BUILD_NAT, test "x$osmo_ac_build_nat" = "xyes")
+AC_SUBST(osmo_ac_build_nat)
 
 AC_ARG_ENABLE([osmo-bsc], [AS_HELP_STRING([--enable-osmo-bsc], [Build the Osmo BSC])],
     [
@@ -106,6 +107,7 @@
     src/libgb/Makefile
     src/gprs/Makefile
     tests/Makefile
+    tests/atlocal
     tests/debug/Makefile
     tests/gsm0408/Makefile
     tests/db/Makefile
diff --git a/openbsc/tests/Makefile.am b/openbsc/tests/Makefile.am
index 73e8b89..9722b14 100644
--- a/openbsc/tests/Makefile.am
+++ b/openbsc/tests/Makefile.am
@@ -2,14 +2,11 @@
 
 if BUILD_NAT
 SUBDIRS += bsc-nat
-ENABLE_NAT_TEST = echo 'm4_define([ENABLE_NAT_TEST], [1])';
-else
-ENABLE_NAT_TEST = echo '';
 endif
 
 
 # The `:;' works around a Bash 3.2 bug when the output is not writeable.
-$(srcdir)/package.m4: $(top_srcdir)/configure.ac $(top_builddir)/config.log
+$(srcdir)/package.m4: $(top_srcdir)/configure.ac
 	:;{ \
                echo '# Signature of the current package.' && \
                echo 'm4_define([AT_PACKAGE_NAME],' && \
@@ -24,7 +21,6 @@
                echo '  [$(PACKAGE_BUGREPORT)])'; \
                echo 'm4_define([AT_PACKAGE_URL],' && \
                echo '  [$(PACKAGE_URL)])'; \
-               $(ENABLE_NAT_TEST) \
              } >'$(srcdir)/package.m4'
 
 EXTRA_DIST = testsuite.at $(srcdir)/package.m4 $(TESTSUITE)
diff --git a/openbsc/tests/atlocal.in b/openbsc/tests/atlocal.in
new file mode 100644
index 0000000..0ce168b
--- /dev/null
+++ b/openbsc/tests/atlocal.in
@@ -0,0 +1 @@
+enable_nat_test='@osmo_ac_build_nat@'
diff --git a/openbsc/tests/testsuite.at b/openbsc/tests/testsuite.at
index fb57d07..22f0b74 100644
--- a/openbsc/tests/testsuite.at
+++ b/openbsc/tests/testsuite.at
@@ -31,9 +31,9 @@
 AT_CHECK([$abs_top_builddir/tests/gprs/gprs_test], [], [expout], [ignore])
 AT_CLEANUP
 
-m4_ifdef([ENABLE_NAT_TEST],[
 AT_SETUP([bsc-nat])
 AT_KEYWORDS([bsc-nat])
+AT_CHECK([test "$enable_nat_test" != no || exit 77])
 cat $abs_srcdir/bsc-nat/bsc_nat_test.ok > expout
 AT_CHECK([$abs_top_builddir/tests/bsc-nat/bsc_nat_test], [], [expout], [ignore])
-AT_CLEANUP])
+AT_CLEANUP