cmake: remove THIS_IS_NOT_A_DEBUG_BUILD hack

New PCH implementation doesn't use the hacky code that needed this
workaround.

Author: slipher

cmake/DaemonFlags.cmake

@@ -695,8 +695,4 @@ endif()
 
 # Configuration specific definitions
 
-# This stupid trick to define THIS_IS_NOT_A_DEBUG_BUILD (rather than nothing) in the non-debug case
-# is so that it doesn't break the hacky gcc/clang PCH code which reads all the definitions
-# and prefixes "-D" to them.
-set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS
-             $<$<NOT:${DEBUG_GENEXP_COND}>:THIS_IS_NOT_A_>DEBUG_BUILD)
+set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS $<${DEBUG_GENEXP_COND}:DEBUG_BUILD>)