misc NRF52 fixes

src/bare/main-nrf52.cpp

@@ -0,0 +1,13 @@
+#include <assert.h>
+
+static inline void debugger_break(void)
+{
+    __asm volatile("bkpt #0x01\n\t"
+                   "mov pc, lr\n\t");
+}
+
+// handle standard gcc assert failures
+void __attribute__((noreturn)) __assert_func(const char *file, int line, const char *func, const char *failedexpr)
+{
+    debugger_break();
+}