fix build of proxy contract

contracts/proxy/CMakeLists.txt

@@ -2,7 +2,7 @@ file(GLOB ABI_FILES "*.abi")
 configure_file("${ABI_FILES}" "${CMAKE_CURRENT_BINARY_DIR}" COPYONLY)
 
 add_wast_executable(TARGET proxy
-  INCLUDE_FOLDERS "${STANDARD_INCLUDE_FOLDERS}"
+  INCLUDE_FOLDERS "${STANDARD_INCLUDE_FOLDERS}" /usr/local/include
   LIBRARIES libc++ libc eosiolib
   DESTINATION_FOLDER ${CMAKE_CURRENT_BINARY_DIR}
 )