[libbacktrace] Use getexecname() on Solaris

[Uros Bizjak]

Hello!

> With the strnlen-related Go failures now gone on Solaris, another issue
> crept up: several tests were failing like this:
>
> throw: /proc/self/exe
>
> goroutine 4 [running]:
> panic during panic
> FAIL: log
>
> This is due to the hardcoded use of /proc/self/exe in libbacktrace,
> which doesn't exist on Solaris, and probably is also missing on other
> non-Linux OSes.  Solaris (since 2.6, it seems) provides getexecname()
> instead, which this patch uses.

+# Check for getexecname function.
+if test -n "${with_target_subdir}"; then
+   case "${host}" in
+   *-*-solaris2*) have_getexecname=yes ;;
+   *) have_getexecname=no ;;
+   esac
+else
+  AC_CHECK_FUNC(getexecname, [have_getexecname=yes], [have_getexename=no])

There is a typo in the above line, s/have_getexename/have_getexecname

Uros.