CMake -Dassert=true properly enables asserts in Release:

* CMake defaults CMAKE_CXX_FLAGS_RELEASE, etc. to include defining
  NDEBUG, regardless of other options set elsewhere, for most or all
  generators. This change explicitly removes that flag from the relevant
  variables.
* Also move the project command earlier, since it wipes out some local
  changes.

CMakeLists.txt

@@ -54,6 +54,10 @@
 
 cmake_minimum_required(VERSION 3.1.0)
 
+# The project command can override some computed values.
+# Don't put any code above this line.
+project(rippled)
+
 if("${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_BINARY_DIR}")
   set(dir "build")
   set(cmd "cmake")
@@ -96,8 +100,6 @@ endif()
 
 setup_build_cache()
 
-project(rippled)
-
 if(nonunity)
     get_cmake_property(allvars VARIABLES)
     string(REGEX MATCHALL "[^;]*(DEBUG|RELEASE)[^;]*" matchvars "${allvars}")