[CMAKE] Rely less on CMAKE_BUILD_TYPE variable

Having conditional statements with CMAKE_BUILD_TYPE is an antipattern
See https://stackoverflow.com/questions/66079007/having-conditional-statements-on-build-type-variable-a-good-design

We use both single- and multi-config generators (Ninja and VS), so we
can't really rely on CMAKE_BUILD_TYPE, because it's not always set.

This commit alters some conditional flags to use <$CONFIG:...>
generator expression, but is still not complete. Also, our default
optimization level (4) now has what was always a de-facto flags

CMakeLists.txt

@@ -49,6 +49,16 @@ else()
     set(WINARCH ${ARCH})
 endif()
 
+# set CMAKE_BUILD_TYPE if not set
+if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
+    message(STATUS "Setting build type to Debug as none was specified.")
+    set(CMAKE_BUILD_TYPE "Debug" CACHE
+        STRING "Choose the type of build." FORCE)
+    # Set the possible values of build type for cmake-gui
+    set_property(CACHE CMAKE_BUILD_TYPE PROPERTY STRINGS
+                 "Debug" "Release" "MinSizeRel" "RelWithDebInfo")
+endif()
+
 # Versioning
 include(sdk/include/reactos/version.cmake)