build: add requirement for openssl to configure_ac

Add requirement for openssl to configure_ac so that configure will fail
when not found.

Tested: Verified OPENSSL_LIBS contained (-lssl -lcrypto).
Change-Id: I7cf3c671749801f089054be3828e9c3dea564157
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/configure.ac b/configure.ac
index da35058..6eec985 100644
--- a/configure.ac
+++ b/configure.ac
@@ -19,6 +19,7 @@
 AX_APPEND_COMPILE_FLAGS([-Wall -Werror], [CXXFLAGS])
 
 # Check for libraries
+AX_CHECK_OPENSSL([], [AC_MSG_ERROR(["openssl required and not found"])])
 PKG_CHECK_MODULES([PHOSPHOR_DBUS_INTERFACES], [phosphor-dbus-interfaces],,\
     AC_MSG_ERROR(["Requires phosphor-dbus-interfaces package."]))
 PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus],,