Add GC source files

src/Native/gc/CMakeLists.txt

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+project(clrgc)
+
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+
+include_directories(env)
+
+set(SOURCES
+    gccommon.cpp
+    gceewks.cpp
+    gcscan.cpp
+    gcwks.cpp
+    handletable.cpp
+    handletablecache.cpp
+    handletablecore.cpp
+    handletablescan.cpp
+    objecthandle.cpp
+)
+
+if(WIN32)
+    list(APPEND SOURCES
+        env/gcenv.windows.cpp)
+else()
+    list(APPEND SOURCES
+        env/gcenv.unix.cpp)
+endif()
+
+if(CLR_CMAKE_PLATFORM_ARCH_AMD64)
+  add_definitions(-D_TARGET_AMD64_=1)
+  add_definitions(-D_WIN64=1)
+elseif(CLR_CMAKE_PLATFORM_ARCH_I386)
+  add_definitions(-D_TARGET_X86_=1)
+  add_definitions(-D_WIN32=1)
+elseif(CLR_CMAKE_PLATFORM_ARCH_ARM)
+  add_definitions(-D_TARGET_ARM_=1)
+  add_definitions(-D_WIN32=1)
+elseif(CLR_CMAKE_PLATFORM_ARCH_ARM64)
+  add_definitions(-D_TARGET_ARM64_=1)
+  add_definitions(-D_WIN64=1)
+else()
+  clr_unknown_arch()
+endif()
+
+add_compile_options(-Wno-format)
+add_compile_options(-Wno-unused-variable)
+add_compile_options(-Wno-unused-private-field)
+add_compile_options(-Wno-tautological-undefined-compare)
+
+add_library(clrgc STATIC ${SOURCES})
+

src/Native/gc/env/common.cpp

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+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information. 
+//
+
+// common.cpp : source file that includes just the standard includes
+// GCSample.pch will be the pre-compiled header
+// common.obj will contain the pre-compiled type information
+
+#include "common.h"

src/Native/gc/env/common.h

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+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information. 
+//
+
+// common.h : include file for standard system include files,
+// or project specific include files that are used frequently, but
+// are changed infrequently
+//
+
+#pragma once
+
+#define _CRT_SECURE_NO_WARNINGS
+
+#include <stdint.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <wchar.h>
+#include <assert.h>
+#include <stdarg.h>
+#include <memory.h>
+
+#include <new>
+
+#ifndef WIN32
+#include <pthread.h>
+#endif
+
+using namespace std;