交叉编译libptytty

libptytty是rxvt的依赖.

1,修改cmakelist，增加：

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm64)

set(tools /home/tong/arm-gnu-toolchain-14.2.rel1-x86_64-aarch64-none-linux-gnu)
set(CMAKE_C_COMPILER ${tools}/bin/aarch64-none-linux-gnu-gcc)
set(CMAKE_CXX_COMPILER ${tools}/bin/aarch64-none-linux-gnu-g++)

2,cmake .

3,make