ggml : add option to not print stack on abort (ggml/1081)

* Add option to not print stack on abort

Add option/envvar to disable stack printing on abort.
Also link some unittests with Threads to fix link errors on
ubuntu/g++11.

* Update ggml/src/ggml.c

---------

Co-authored-by: Diego Devesa <slarengh@gmail.com>

ggml/src/ggml.c

@@ -128,6 +128,10 @@ static void ggml_print_backtrace_symbols(void) {
 #endif
 
 static void ggml_print_backtrace(void) {
+    const char * GGML_NO_BACKTRACE = getenv("GGML_NO_BACKTRACE");
+    if (GGML_NO_BACKTRACE) {
+        return;
+    }
     char attach[32];
     snprintf(attach, sizeof(attach), "attach %d", getpid());
     int pid = fork();