libcamera: base: backtrace: Use libunwind when available

libunwind is an alternative to glibc's backtrace() to extract a
backtrace. Use it when available to extend backtrace support to more
platforms.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

include/libcamera/base/backtrace.h

@@ -26,6 +26,9 @@ public:
 private:
 	LIBCAMERA_DISABLE_COPY(Backtrace)
 
+	bool backtraceTrace();
+	bool unwindTrace();
+
 	std::vector<void *> backtrace_;
 };