Factor out shared backtrace code (#1793)

src/backtrace.cpp

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: MIT
+
+#include "backtrace.hpp"
+
+#include <stdlib.h> // strtoul
+
+#include "platform.hpp" // strcasecmp
+
+uint64_t traceDepth = 0;
+
+bool trace_ParseTraceDepth(char const *arg) {
+	if (!strcasecmp(arg, "collapse")) {
+		traceDepth = TRACE_COLLAPSE;
+		return true;
+	}
+
+	char *endptr;
+	traceDepth = strtoul(arg, &endptr, 0);
+
+	return arg[0] != '\0' && *endptr == '\0' && traceDepth != TRACE_COLLAPSE;
+}