Suggest --disable-wallet when libdb_cxx headers are missing

build-aux/m4/bitcoin_find_bdb48.m4

@@ -38,7 +38,7 @@ AC_DEFUN([BITCOIN_FIND_BDB48],[
   done
   if test "x$bdbpath" = "xX"; then
     AC_MSG_RESULT([no])
-    AC_MSG_ERROR(libdb_cxx headers missing)
+    AC_MSG_ERROR([libdb_cxx headers missing, Bitcoin Core requires this library for wallet functionality (--disable-wallet to disable wallet functionality)])
   elif test "x$bdb48path" = "xX"; then
     BITCOIN_SUBDIR_TO_INCLUDE(BDB_CPPFLAGS,[${bdbpath}],db_cxx)
     AC_ARG_WITH([incompatible-bdb],[AS_HELP_STRING([--with-incompatible-bdb], [allow using a bdb version other than 4.8])],[