Build fix: missing error_get_str on non-glibc builds

Build fix: missing error_get_str on non-glibc builds

The function declaration was erroneously moved inside this ifdef. This
breaks non glibc builds.

Introduced in :

  commit 003f455dab0204dd3f066ecdbea0470035f8181f
  Author: Jérémie Galarneau <jeremie.galarneau@efficios.com>
  Date:   Thu Apr 13 14:31:33 2023 -0400

    Fix: logging: unhandled error in *_FMT macros

    Coverity reports:

    1508779 Uncaught exception
    If the exception is ever thrown, the program will crash.

    In lttng::​sessiond::​rotation_thread::​_thread_function(): A C++ exception
    is thrown but never caught (CWE-248)

    The *_FMT macros, which use fmtlib, don't handle the case where
    fmt::format throws. This can happen, in particular, when an invalid
    format string is used.

    The macros are modified to log the exception and abort.

Change-Id: I5eb3b2a673e224f3c99cae7faece31175084db9d
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>