Added CMake build script for libzerotiercore.a

CMakeLists.txt

@@ -0,0 +1,12 @@
+# CMake build script for libzerotiercore.a
+
+cmake_minimum_required (VERSION 2.8)
+project (zerotiercore)
+
+set (PROJ_DIR ${PROJECT_SOURCE_DIR})
+set (ZT_DEFS -std=c++11 "-DZT_SDK=1")
+
+file(GLOB core_src_glob ${PROJ_DIR}/node/*.cpp)
+add_library(zerotiercore STATIC ${core_src_glob})
+
+target_compile_options(zerotiercore PRIVATE ${ZT_DEFS})