msp432p401lp-cc256x: provide working _sbrk

port/msp432p401lp-cc256x/main.c

@@ -101,9 +101,20 @@ int _fstat(int file){
     return -1;
 }
 
+extern int _end;
+
 void * _sbrk(int incr){
-    UNUSED(incr);
-    return NULL;
+    static unsigned char *heap = NULL;
+    unsigned char *prev_heap;
+
+    if (heap == NULL) {
+        heap = (unsigned char *)&_end;
+    }
+    prev_heap = heap;
+
+    heap += incr;
+
+    return prev_heap;
 }
 #endif