cmake : add msvc compiler args /utf-8 fix error C3688 (#721)

* force msvc compiler use utf-8 encode

* only enable on msvc

CMakeLists.txt

@@ -2,6 +2,10 @@ cmake_minimum_required (VERSION 3.0)
 
 project(whisper.cpp VERSION 1.2.1)
 
+if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
+    add_compile_options(/utf-8)
+endif ()
+
 # Add path to modules
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/")