Many platforms don't support backtraces. Fix compile for Solaris platform.
This change was tested with Solaris 10 on X86 and SPARC.
More information on Unix Backtrace Support
- http://www.gnu.org/software/libc/manual/html_node/Backtraces.html
It is not supported on the following platforms:
- https://www.gnu.org/software/gnulib/manual/html_node/execinfo_002eh.html
Mac OS X 10.3,
FreeBSD 6.0,
NetBSD 5.0,
OpenBSD 3.8,
Minix 3.1.8,
AIX 5.1,
HP-UX 11,
IRIX 6.5,
OSF/1 5.1,
Solaris 10,
Cygwin,
mingw,
MSVC 9,
Interix 3.5,
BeOS.