xplat: add ChakraCoreHeaders target.

This target automatically copies the ChakraCore Headers to the the path
that cmake is ran from under the include folder. This makes it easier to
find the headers needed for ChakraCore Development.

V2: add suggestions mentioned by review in pull request chakra-core#2129.

bin/ChakraCore/CMakeLists.txt

@@ -155,4 +155,8 @@ if(NOT CC_XCODE_PROJECT)
     "${CHAKRACORE_BINARY_DIR}/bin/ChakraCore/libChakraCoreStatic.a"
     "${CHAKRACORE_BINARY_DIR}/"
     )
+  if(TARGET ChakraCoreHeaders)
+    add_dependencies(ChakraCore ChakraCoreHeaders)
+    add_dependencies(ChakraCoreStatic ChakraCoreHeaders)
+  endif()
 endif()

lib/Jsrt/CMakeLists.txt

@@ -57,3 +57,19 @@ target_include_directories (
     ../Runtime/Debug
     ../Parser
     )
+
+if(NOT CC_XCODE_PROJECT)
+  add_custom_target(ChakraCoreHeaders ALL
+  COMMAND ${CMAKE_COMMAND} -E make_directory
+    "${CMAKE_BINARY_DIR}/include"
+  COMMAND ${CMAKE_COMMAND} -E copy_if_different
+    "${CMAKE_CURRENT_SOURCE_DIR}/ChakraCore.h"
+    "${CMAKE_BINARY_DIR}/include"
+  COMMAND ${CMAKE_COMMAND} -E copy_if_different
+    "${CMAKE_CURRENT_SOURCE_DIR}/ChakraCommon.h"
+    "${CMAKE_BINARY_DIR}/include"
+  COMMAND ${CMAKE_COMMAND} -E copy_if_different
+    "${CMAKE_CURRENT_SOURCE_DIR}/ChakraDebug.h"
+    "${CMAKE_BINARY_DIR}/include"
+  )
+endif()