As in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86113 for
__builtin_nan, bits/mathcalls.h wrongly declares the nan function with
the __const__ attribute. Because the function reads memory pointed to
by an argument, it's only pure, not const. This patch removes the
incorrect attribute and adds a testcase for the bug. No __pure__
attribute is added to replace the incorrect __const__ one, since that
would introduce problems when using GCC versions that have the
incorrect built-in __const__ attribute and warn for the combination of
those two attributes.
Tested for x86_64.
[BZ #23277]
* math/bits/mathcalls.h [__USE_ISOC99] (nan): Do not use __const__
attribute.
* math/test-nan-const.c: New file.
* math/Makefile (tests): Add test-nan-const.
(CFLAGS-test-nan-const.c): New variable.
