group-member: Declare function in <unistd.h>. * lib/unistd.in.h (group_member): New declaration. * lib/group-member.h: Remove file. * lib/group-member.c: Include <unistd.h> instead of group-member.h. * tests/test-unistd-c++.cc: Check signature of group_member. * m4/group-member.m4 (gl_FUNC_GROUP_MEMBER): Require gl_UNISTD_H_DEFAULTS. Set HAVE_GROUP_MEMBER. * m4/unistd_h.m4 (gl_UNISTD_H): Check whether group_member is declared. (gl_UNISTD_H_DEFAULTS): Initialize GNULIB_GROUP_MEMBER, HAVE_GROUP_MEMBER. * modules/group-member (Files): Remove lib/group-member.h. (Depends-on): Add unistd. Specify conditions. (configure.ac): Invoke gl_UNISTD_MODULE_INDICATOR. (Include): Change to <unistd.h>. * modules/unistd (Makefile.am): Substitute GNULIB_GROUP_MEMBER, HAVE_GROUP_MEMBER. * NEWS: Mention the change. * lib/euidaccess.c: Don't include group-member.h.