cmake: Set uninitialized variable warnings in ULP & bootloader subprojects

Fixes issue where PYTHON was not being expanded when running ulp_mapgen.py,
causing Windows launch setting to be used - reported here:
https://esp32.com/viewtopic.php?f=13&t=12640&p=50283#p50283

Closes https://github.com/espressif/esp-idf/issues/4785

tools/idf.py

@@ -236,6 +236,7 @@ def _ensure_build_directory(args, always_run_cmake=False):
             ]
             if not args.no_warnings:
                 cmake_args += ["--warn-uninitialized"]
+                cmake_args += ["-DWARN_UNINITIALIZED=1"]
 
             if args.define_cache_entry:
                 cmake_args += ["-D" + d for d in args.define_cache_entry]