[Bug other/58312] libssp configure check for "usable vsnprintf" is broken on cross-compilers.

["joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58312

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
If your target uses glibc, you don't need libssp anyway.

libssp is used by LINK_SSP_SPEC if TARGET_LIBC_PROVIDES_SSP is not 
defined.  TARGET_LIBC_PROVIDES_SSP is defined when glibc headers are 
available when configuring GCC, and they are version 2.4 or later (or some 
other conditions for some other C libraries).

The checks for headers do cause problems when bootstrapping a cross 
toolchain - you may need to set gcc_cv_libc_provides_ssp=yes to get a 
correctly configured bootstrap compiler that can build glibc.  See 
<http://gcc.gnu.org/ml/gcc/2013-06/msg00112.html> for how I think that 
should be fixed - a configure option to specify the target glibc version.

If your target does not use glibc, I have no advice beyond the general 
principle that the default should be assuming a function works and then 
known-broken systems (if any are supported) can be blacklisted.