Add a basic sample to show how native runtime invokes wasm apps in WAMR and how wasm apps invoke native functions. (#207)

* Add printingAdd print time for wamrc, fix posix mmap bug time for wamrc, fixed a posix mmap bug.

Change-Id: Ib6517b8a69cf022a1a6a74efa1f98155aec143bc

* Add a basic sample to show how native runtime invokes wasm app in WAMR, and how wasm app invokes native functions.

Change-Id: I700ae413ad5e9ea04540d5187952305e1ee92d73

samples/basic/wasm-apps/testapp.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2019 Intel Corporation.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int intToStr(int x, char* str, int str_len, int digit);
+int get_pow(int x, int y);
+
+//
+// Primitive parameters functions
+//
+float generate_float(int iteration, double seed1, float seed2)
+{
+    float ret;
+
+    printf ("calling into WASM function: %s\n", __FUNCTION__);
+
+    for (int i=0; i<iteration; i++){
+        ret += 1.0f/seed1 + seed2;
+    }
+
+    return ret;
+}
+
+// Converts a floating-point/double number to a string.
+// intToStr() is implemented outside wasm app
+void float_to_string(float n, char* res, int res_size, int afterpoint)
+{
+
+    printf ("calling into WASM function: %s\n", __FUNCTION__);
+
+    // Extract integer part
+    int ipart = (int)n;
+
+    // Extract floating part
+    float fpart = n - (float)ipart;
+
+    // convert integer part to string
+    int i = intToStr(ipart, res, res_size, 0);
+
+    // check for display option after point
+    if (afterpoint != 0) {
+        res[i] = '.'; // add dot
+
+        // Get the value of fraction part upto given no.
+        // of points after dot. The third parameter
+        // is needed to handle cases like 233.007
+        fpart = fpart * get_pow(10, afterpoint);
+
+        intToStr((int)fpart, res + i + 1, sizeof(res + i + 1), afterpoint);
+    }
+}