[2.0.x] Move backtrace to a shared location (#10237)

- And implement the `backtrace()` function call

Marlin/src/backtrace/unwinder.cpp

@@ -0,0 +1,61 @@
+/***************************************************************************
+ * ARM Stack Unwinder, Michael.McTernan.2001@cs.bris.ac.uk
+ * Updated, adapted and several bug fixes on 2018 by Eduardo José Tagle
+ *
+ * This program is PUBLIC DOMAIN.
+ * This means that there is no copyright and anyone is able to take a copy
+ * for free and use it as they wish, with or without modifications, and in
+ * any context, commercially or otherwise. The only limitation is that I
+ * don't guarantee that the software is fit for any purpose or accept any
+ * liability for it's use or misuse - this software is without warranty.
+ ***************************************************************************
+ * File Description: Implementation of the interface into the ARM unwinder.
+ **************************************************************************/
+
+#if defined(__arm__) || defined(__thumb__)
+
+#define MODULE_NAME "UNWINDER"
+
+#include <stdio.h>
+#include <string.h>
+#include "unwinder.h"
+#include "unwarm.h"
+#include "unwarmbytab.h"
+
+/* These symbols point to the unwind index and should be provide by the linker script */
+extern "C" const UnwTabEntry __exidx_start[];
+extern "C" const UnwTabEntry __exidx_end[];
+
+// Detect if unwind information is present or not
+static int HasUnwindTableInfo(void) {
+  // > 16 because there are default entries we can´t supress
+  return ((char*)(&__exidx_end) - (char*)(&__exidx_start)) > 16 ? 1 : 0;
+}
+
+UnwResult UnwindStart(UnwindFrame* frame, const UnwindCallbacks *cb, void *data) {
+
+  if (HasUnwindTableInfo()) {
+
+    /* We have unwind information tables */
+    return UnwindByTableStart(frame, cb, data);
+
+  } else {
+
+    /* We don't have unwind information tables */
+    UnwState state;
+
+    /* Initialise the unwinding state */
+    UnwInitState(&state, cb, data, frame->pc, frame->sp);
+
+    /* Check the Thumb bit */
+    if(frame->pc & 0x1) {
+      return UnwStartThumb(&state);
+    }
+    else {
+      return UnwStartArm(&state);
+    }
+  }
+}
+#endif
+
+