[vfs] Add debug-only check to prevent `return` in some VFS funcs
[vfs] Add debug-only check to prevent `return` in some VFS funcs

VFS functions using the macros VFS_FS_PATH_FUNCS_COMMON_HEADER() and
VFS_FS_PATH_FUNCS_COMMON_FOOTER() must *not* return bypassing the footer.
Doing that by mistake would lead to nasty bugs. In order to prevent that,
a nice compiler trick has been used (the attribute cleanup) to check against
a return statement bypassing the footer.

vvaltchev/experimentOs,vvaltchev/experimentOs,vvaltchev/experimentOs,vvaltchev/experimentOs