The sources for Chez Scheme come in two parts:

* A set of Scheme source files found in the subdirectory s.  Compiling
  these produces the boot files petite.boot and scheme.boot, along with
  two header files, equates.h and scheme.h.

* A set of C source files found in the subdirectory c.  Compiling and
  linking these files produces the executable scheme (scheme.exe under
  Windows).  Compiling the C sources requires the two header files
produced by compiling the Scheme sources.

Actually it's in the release notes of glibc:

    4.1. Removal of 'xlocale.h'

    The nonstandard header xlocale.h has been removed in this release. It was never intended to be included directly by programs other than glibc itself, and it was a strict subset of the standard header locale.h. We know that a number of programs do include it, but because it has never been part of any other C library, programs that use it are probably testing for its existence with autoconf or a similar tool, and should not fail to compile.

dse@susepc:~/cs/csv9.5$ strings /usr/bin/scheme|grep clang
clang version 4.0.1-10 (tags/RELEASE_401/final)