BUILD: Use LTO by default for everything but Debug builds

Instead of relying on explicitly having to use the "Release" target, we
now enable LTO for everything but the special "Debug" target. That is,
we assume that every configuration other than "Debug" is likely meant as
some sort of release build (potentially with external flags) and thus
we want to make use of LTO.

CMakeLists.txt

@@ -161,7 +161,8 @@ add_compile_definitions(MUMBLE_TARGET_OS="${MUMBLE_TARGET_OS}")
 
 
 set(CMAKE_UNITY_BUILD_BATCH_SIZE 40)
-set(CMAKE_INTERPROCEDURAL_OPTIMIZATION_RELEASE ${lto})
+set(CMAKE_INTERPROCEDURAL_OPTIMIZATION ${lto})
+set(CMAKE_INTERPROCEDURAL_Debug OFF)
 
 if(client OR server)
 	add_subdirectory(src)