Don't try to use lchmod() on linux, glibc has only a stub of lchmod(). Remove defines for XSH4.2 UNIX extensions from the test for lchmod(), there is no lchmod() in XSH4.2 and rbx is also not compiled with these defines.
Remove defines for XSH4.2 UNIX extensions from the test for lchown(), rbx is not compiled with these defines.
Merge pull request #2825 from r-stu31/configure_lchomd_lchown

Fix detection of lchmod() and lchown() in "configure" script