Some Windows and MSVC fixes (#4569)

* fix python exception creation in Windows

* better string conversion for msvc

* fix cpp style issue

python/tvm/_ffi/base.py

@@ -35,8 +35,13 @@ if sys.version_info[0] == 3:
     # this function is needed for python3
     # to convert ctypes.char_p .value back to python str
     if sys.platform == "win32":
+        def _py_str(x):
+            try:
+                return x.decode('utf-8')
+            except UnicodeDecodeError:
                 encoding = 'cp' + str(ctypes.cdll.kernel32.GetACP())
-        py_str = lambda x: x.decode(encoding)
+                return x.decode(encoding)
+        py_str = _py_str
     else:
         py_str = lambda x: x.decode('utf-8')
 else:

src/runtime/c_runtime_api.cc

@@ -235,7 +235,14 @@ std::string NormalizeError(std::string err_msg) {
     if (!(is >> line)) return false;
     // get filename
     while (is.peek() == ' ') is.get();
+#ifdef _MSC_VER  // handle volume separator ":" in Windows path
+    std::string drive;
+    if (!getline(is, drive, ':')) return false;
     if (!getline(is, file_name, ':')) return false;
+    file_name = drive + ":" + file_name;
+#else
+    if (!getline(is, file_name, ':')) return false;
+#endif
     // get line number
     if (!(is >> line_number)) return false;
     // get rest of the message.