[compiler-rt] fix build on Illumos

- there are additional fields for glob_t struct, thus size check is failing.
- to access old mman.h api based on caddr_t, _XOPEN_SOURCE needs to be not defined
 thus we provide the prototype.
- prxmap_t constified.

Reviewers: ro, eugenis

Reviewed-By: ro

Differential Revision: https://reviews.llvm.org/D84046