[fix] codestyle & msvc warnings

CMakeLists.txt

@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-cmake_minimum_required(VERSION 3.9)
+cmake_minimum_required(VERSION 3.1)
 project(leveldb VERSION 1.21.0 LANGUAGES C CXX)
 
 # This project can use C11, but will gracefully decay down to C89.
@@ -79,6 +79,12 @@ if(BUILD_SHARED_LIBS)
   add_compile_options(-fvisibility=hidden)
 endif(BUILD_SHARED_LIBS)
 
+if (MSVC)
+  add_compile_options (/wd4244 /wd4996 /wd4018 /MP)
+#  add_compile_options ("/MP")
+endif()
+
+
 add_library(leveldb "")
 target_sources(leveldb
   PRIVATE

port/atomic_pointer.h

@@ -33,9 +33,14 @@ namespace leveldb {
   typedef intptr_t ssize_t;
 }
 #endif
+
+#ifdef DeleteFile
 #undef DeleteFile
+#endif
+#ifdef small
 #undef small
 #endif
+#endif
 
 #if defined(_M_X64) || defined(__x86_64__)
 #define ARCH_CPU_X86_FAMILY 1