Add _IO_stdin_used in version-script to fix SIGBUSes on Sparc.

The --version-script,asterisk.exports linker flag (and the module
exports) didn't provide _IO_stdin_used in the list of exported symbols.
That causes some kind of libc compatibility mode to kick in, where
stdio file structures (stdout/stderr) land somewhere else. In the
case of the Sparc, they landed on misaligned memory.

This became apparent first after r376428 (Reorder startup sequence)
when a lot of ast_log's were replaced with fprintf's. Writing to
stderr triggered a SIGBUS. (Compared to x86 and amd64 architectures,
the Sparc is very picky about memory alignment.)

(issue ASTERISK-21763)
(issue ASTERISK-21665)

Reported by: Jeremy Kister
Review: https://reviewboard.asterisk.org/r/2760/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@397377 f38db490-d61c-443f-a65b-d21fe96a405b