build: always define conditionals

Always define conditionals to enable building of Makefiles.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: Id8786d3d5ec6b1ce4582043d6a331921911963d8
diff --git a/configure.ac b/configure.ac
index 40df159..e82aca7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -117,6 +117,9 @@
     AS_IF([test "x$enable_host_bios" = "xyes"], [
         AX_APPEND_COMPILE_FLAGS([-DENABLE_HOST_BIOS], [CXXFLAGS])
     ])
+], [
+    AM_CONDITIONAL([HAVE_SYSTEMD], [0])
+    AM_CONDITIONAL([ENABLE_HOST_BIOS], [0])
 ])
 
 # If not building the host-tool, we're building the BMC.