ggml : Print backtrace on uncaught C++ exceptions (ggml/1232)

The goal is to have what users call "full logs" contain the backtrace.

This is registered upon ggml_init. Also fixes a minor fd leak on Linux.

ggml/src/ggml-impl.h

@@ -32,6 +32,8 @@
 extern "C" {
 #endif
 
+void ggml_print_backtrace(void);
+
 #ifndef MIN
 #    define MIN(a, b) ((a) < (b) ? (a) : (b))
 #endif