+ error: avoid expand-before-require warning
+ * modules/errno (configure.ac): Require, rather than expand,
+ gl_HEADER_ERRNO_H.
+ * m4/errno_h.m4 (gl_HEADER_ERRNO_H_BODY): Merge...
+ (gl_HEADER_ERRNO_H): ...into this macro, and use AC_DEFUN_ONCE to
+ enforce that all clients require it.
+