Is this really needed? Config file already have parenthesis around SPIFFS_CACHE_WR, SPIFFS_CACHE_STATS defines, so if SPIFFS_CACHE is not defined - SPIFFS_CACHE_WR and SPIFFS_CACHE_STATS will not be defined too.

Config has parenthesis, but source files use
#if SPIFFS_CACHE_WR
so this results in a warning -Wundef.
Personally I like to compile with -Werror which fails the compile for me.
As an alternative changing to
#if defined(SPIFFS_CACHE_WR)
should also silence the -Wundef warning, where we are being more explicit if the macro was defined at all.