The implementation of "real_path()" was to go there with chdir(2)
and call getcwd(3), but this obviously wouldn't be usable in a
threaded environment. Rewrite it to manually resolve relative
paths including symbolic links in path components.
* bw/realpath-wo-chdir:
real_path: set errno when max number of symlinks is exceeded
real_path: prevent redefinition of MAXSYMLINKS