The idf_path variable was used in -fmacro-prefix-map and
-fdebug-prefix-map flags but never read from the IDF_PATH build
property, resulting in an empty substitution. This caused full
filesystem paths to leak into .rodata instead of being mapped to /IDF.
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>