查找ASPELL

尝试找到 ASPELL

一旦完成，这将定义

ASPELL_FOUND - system has ASPELL
ASPELL_EXECUTABLE - the ASPELL executable
ASPELL_INCLUDE_DIR - the ASPELL include directory
ASPELL_LIBRARIES - The libraries needed to use ASPELL
ASPELL_DEFINITIONS - Compiler switches required for using ASPELL