gdb: workaround sparc memcpy fortify error

gdb: workaround sparc memcpy fortify error

Building on an x86_64-linux system with --enable-targets=all fails on the
sparc code with a fortify error:

cc1: warnings being treated as errors
In file included from /usr/include/string.h:640,
                 from gnulib/string.h:23,
                 from ../../gdb/gdb_string.h:25,
                 from ../../gdb/vec.h:25,
                 from ../../gdb/memattr.h:24,
                 from ../../gdb/target.h:60,
                 from ../../gdb/exec.h:23,
                 from ../../gdb/gdbcore.h:31,
                 from ../../gdb/sparc-tdep.c:29:
In function 'memcpy',
    inlined from 'sparc32_store_return_value' at ../../gdb/sparc-tdep.c:1112,
    inlined from 'sparc32_return_value' at ../../gdb/sparc-tdep.c:1170:
/usr/include/bits/string3.h:52: error: call to __builtin___memcpy_chk will
        always overflow destination buffer
make: *** [sparc-tdep.o] Error 1

This is due to the gcc optimizer bug PR37060, so tweak the gdb_assert ()
to avoid the issue.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>