build: set build type and per-build-type flags as early as possible

With the exception of the first c++ checks, this ensures that compiler tests
are never run with the wrong build type's flags.

Co-Authored-By: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

cmake/module/ProcessConfigurations.cmake

@@ -4,8 +4,6 @@
 
 include_guard(GLOBAL)
 
-include(TryAppendCXXFlags)
-
 macro(normalize_string string)
   string(REGEX REPLACE " +" " " ${string} "${${string}}")
   string(STRIP "${${string}}" ${string})
@@ -119,6 +117,8 @@ endfunction()
 
 set_default_config(RelWithDebInfo)
 
+include(TryAppendCXXFlags)
+
 # We leave assertions on.
 if(MSVC)
   remove_cxx_flag_from_all_configs(/DNDEBUG)