maint: cleanup up various uses of __attribute__
* src/cfg.mk (sc_prohibit-gl-attributes): Disallow the __attribute()
form without trailing underscores as that is not elided where required.
Also ensure we use gnulib macros rather than defining our own.
* src/system.h: Remove gnulib provided macros.
* src/chown-core.c: Likewise.
* src/chroot.c: Likewise.
* src/copy.c: Likewise.
* src/csplit.c: Likewise.
* src/dd.c: Likewise.
* src/expr.c: Likewise.
* src/extent-scan.c: Likewise.
* src/factor.c: Likewise.
* src/ls.c: Likewise.
* src/od.c: Likewise.
* src/paste.c: Likewise.
* src/ptx.c: Likewise.
* src/sort.c: Likewise.
* src/stat.c: Likewise.
* src/stty.c: Likewise.
* src/system.h: Likewise.
* src/tac.c: Likewise.
* src/test.c: Likewise.
* src/tsort.c: Likewise.
13 files changed: