Build: added support for unity builds in most projects except for StormLib, ZLib and Scripts

cmake/options.cmake

@@ -51,4 +51,4 @@ set(WITH_SOURCE_TREE    "hierarchical" CACHE STRING "Build the source tree for I
 set_property(CACHE WITH_SOURCE_TREE PROPERTY STRINGS no flat hierarchical hierarchical-folders)
 option(WITHOUT_GIT      "Disable the GIT testing routines"                            0)
 option(BUILD_TESTING    "Build test suite" 0)
-
+option(UNITY_BUILDS     "Enables the unity build mode which combines multiple source files into buckets to speed up build time" 0)

cmake/showoptions.cmake

@@ -38,6 +38,12 @@ else()
   message("* Build unit tests       : No (default)")
 endif()
 
+if(UNITY_BUILDS)
+  message("* Unity build enabled    : Yes")
+else()
+  message("* Unity build enabled    : No (default)")
+endif()
+
 if(USE_COREPCH)
   message("* Build core w/PCH       : Yes (default)")
 else()