Clean up conditionals for declaration of gets.

gets has the dubious honor of being the only C89 library feature that
has been completely removed from the current C and C++ standards.
glibc follows suit by not declaring it in _GNU_SOURCE mode either,
but it remains present in older compatibility modes.  Internally,
two test cases need to see stdio.h make the declaration, but all our
internal code is of course compiled under _GNU_SOURCE.  This is currently
kludged by duplicating the gets declaration, fortify wrapper and all,
in include/stdio.h.  Also, the conditional in the public headers for
deciding when to declare gets is complicated and repeated in two places.

This patch adds a new macro to features.h that encapsulates the
complicated rule for when to declare gets.  stdio.h and bits/stdio2.h
then simply test __GLIBC_USE (DEPRECATED_GETS), and instead of having
a duplicate gets declaration in include/stdio.h, debug/tst-chk1.c and
stdio-common/tst-gets.c can force gets to be declared.

        * include/features.h (__GLIBC_USE_DEPRECATED_GETS): New macro.
        * libio/stdio.h, libio/bits/stdio2.h: Condition gets on
        __GLIBC_USE (DEPRECATED_GETS).  Update comments to indicate
        gets was removed from C++ in C++14.
        * include/stdio.h: Remove redundant declaration of gets.
        * debug/tst-chk1.c, stdio-common/tst-gets.c: Force gets to
        be declared, since we are testing it.
        * stdio-common/Makefile (tst-gets.c): Compile with
        -Wno-deprecated-declarations.
	* debug/Makefile (tst-chk1.c, tst-chk2.c, tst-chk3.c, tst-chk4.cc)
	(tst-chk5.cc, tst-chk6.cc, tst-lfschk1.c, tst-lfschk2.c)
	(tst-lfschk3.c, tst-lfschk4.cc, tst-lfschk5.cc, tst-lfschk6.cc):
	Compile with -Wno-deprecated-declarations.

2 files changed, 21 insertions, 15 deletions

diff --git a/debug/Makefile b/debug/Makefile
index 3d268f0422..cd4975c35b 100644
--- a/debug/Makefile
+++ b/debug/Makefile
@@ -103,21 +103,22 @@ CFLAGS-tst-longjmp_chk3.c = -fexceptions -fasynchronous-unwind-tables
 CPPFLAGS-tst-longjmp_chk3.c = -D_FORTIFY_SOURCE=1
 
 # We know these tests have problems with format strings, this is what
-# we are testing.  Disable that warning.  They also generate warnings
-# from warning attributes, which cannot be disabled via pragmas, so
-# require -Wno-error to be used.
-CFLAGS-tst-chk1.c = -Wno-format -Wno-error
-CFLAGS-tst-chk2.c = -Wno-format -Wno-error
-CFLAGS-tst-chk3.c = -Wno-format -Wno-error
-CFLAGS-tst-chk4.cc = -Wno-format -Wno-error
-CFLAGS-tst-chk5.cc = -Wno-format -Wno-error
-CFLAGS-tst-chk6.cc = -Wno-format -Wno-error
-CFLAGS-tst-lfschk1.c = -Wno-format -Wno-error
-CFLAGS-tst-lfschk2.c = -Wno-format -Wno-error
-CFLAGS-tst-lfschk3.c = -Wno-format -Wno-error
-CFLAGS-tst-lfschk4.cc = -Wno-format -Wno-error
-CFLAGS-tst-lfschk5.cc = -Wno-format -Wno-error
-CFLAGS-tst-lfschk6.cc = -Wno-format -Wno-error
+# we are testing.  Disable that warning.  They are also testing
+# deprecated functions (notably gets) so disable that warning as well.
+# And they also generate warnings from warning attributes, which
+# cannot be disabled via pragmas, so require -Wno-error to be used.
+CFLAGS-tst-chk1.c = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-chk2.c = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-chk3.c = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-chk4.cc = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-chk5.cc = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-chk6.cc = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-lfschk1.c = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-lfschk2.c = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-lfschk3.c = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-lfschk4.cc = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-lfschk5.cc = -Wno-format -Wno-deprecated-declarations -Wno-error
+CFLAGS-tst-lfschk6.cc = -Wno-format -Wno-deprecated-declarations -Wno-error
 LDLIBS-tst-chk4 = -lstdc++
 LDLIBS-tst-chk5 = -lstdc++
 LDLIBS-tst-chk6 = -lstdc++
diff --git a/debug/tst-chk1.c b/debug/tst-chk1.c
index 164d0ae63e..60c8e1e1d0 100644
--- a/debug/tst-chk1.c
+++ b/debug/tst-chk1.c
@@ -16,6 +16,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
+/* This file tests gets.  Force it to be declared.  */
+#include <features.h>
+#undef __GLIBC_USE_DEPRECATED_GETS
+#define __GLIBC_USE_DEPRECATED_GETS 1
+
 #include <assert.h>
 #include <fcntl.h>
 #include <locale.h>