greatroar 8a1e54d58a lib/fs: Optimize Canonicalize
When pathSep is a constant, the compiler precomputes pathSep+pathSep and
".."+pathSep instead of emitting function calls to compute "//" and
"../". Benchmark results in lib/osutil:

name                old time/op    new time/op    delta
TraversesSymlink-8    8.86µs ± 3%    8.53µs ± 4%  -3.79%  (p=0.000 n=18+20)

name                old alloc/op   new alloc/op   delta
TraversesSymlink-8    1.06kB ± 0%    1.06kB ± 0%    ~     (all equal)

name                old allocs/op  new allocs/op  delta
TraversesSymlink-8      15.0 ± 0%      15.0 ± 0%    ~     (all equal)
2021-11-23 21:25:29 +01:00
..
2021-11-23 21:25:29 +01:00