build: stop on error in check for mapper

The configure check for the mapper repository did not have an error
condition in it.  Therefore, the configure run passed and then the
failure surfaced as a missing header file on compile.  Add an explicit
error condition to the AC_CHECK_LIB call.

Change-Id: Ie7d2941963977ba157d65970db21044e7eec9b6f
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/configure.ac b/configure.ac
index c1ef974..7a74c01 100644
--- a/configure.ac
+++ b/configure.ac
@@ -17,10 +17,11 @@
     [AC_MSG_ERROR([Could not find python-2.7 installed...python-2.7 is required])])
 
 # Checks for libraries.
-AC_CHECK_LIB([mapper], [mapper_get_service])
+AC_CHECK_LIB([mapper], [mapper_get_service],,\
+    [AC_MSG_ERROR([Could not find libmapper: phosphor-objmgr package required])])
 PKG_CHECK_MODULES([SYSTEMD], [libsystemd >= 221])
 PKG_CHECK_MODULES([SDBUSPLUS], [sdbusplus],,\
-    AC_MSG_ERROR(["Requires sdbusplus package."]))
+    [AC_MSG_ERROR([Requires sdbusplus package.])])
 
 # Checks for header files.
 AC_CHECK_HEADER(systemd/sd-bus.h, ,[AC_MSG_ERROR([Could not find systemd/sd-bus.h...systemd development package required])])