Make internal class __wrap_iter constexpr when not using libc++'s debugging mode. Introduce a new macro _LIBCPP_CONSTEXPR_IF_NODEBUG to mark this.

llvm-svn: 337019
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Cr-Mirrored-Commit: 9cad502555b5b0ad5dc3766f7d363db939387fd1
3 files changed