Only write subversion/libsvn_subr/errorcode.inc, when its content has changed instead of on every invocation of gen-make.py.
Visual Studio's dependency checker recompiles files that include this .inc file (read: libsvn_subr). Which then results in relinking libsvn_subr and everything that uses it after every gen-make.py invocation.
* build/generator/gen_base.py (write_file_if_changed): Move helper function from gen_win.py to here. (write_errno_table): To allow using it from this function.
* build/generator/gen_win.py (write_file_if_changed): Remove function here.