Fix trailing-slash mkdir under sysroot

[jserv]

proc_resolve_sysroot_create_path located the leaf separator with strrchr on the resolved sysroot path. A guest path ending in a slash made strrchr match that trailing slash, so the parent buffer collapsed to the target itself. The parent-existence access() then failed and the resolver wrongly fell back to the host literal path (or auto-created the target as if it were its own parent), so mkdir("/dir/") reported ENOENT or EEXIST instead of creating the directory in the sysroot.

Drop trailing slashes before splitting off the leaf so the check sees the real parent. Guard all-slash guest paths ("/", "///") up front: they name the root, which always exists and has no parent, and trimming would otherwise walk strrchr into the sysroot prefix and trip the containment check (ELOOP) on a multi-component sysroot.

Close #100

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Summary by cubic

Fixes trailing-slash handling in sysroot path resolution so mkdir("/dir/") creates the directory under the sysroot instead of returning ENOENT/EEXIST or falling back to the host. Also correctly treats "/", "///" as the root.

• Bug Fixes
  • Trim trailing slashes before splitting the leaf in proc_resolve_sysroot_create_path so the parent check uses the real parent.
  • Handle all-slash guest paths as root and add tests for root mkdir and trailing-slash mkdir under "/tmp" to verify correct routing inside the sysroot.

^{Written for commit fb7bb95. Summary will update on new commits.}

[jserv]

@doanbaotrung , Please validate this PR.

[doanbaotrung]

It worked!