Add x32 ABI support on Linux The x32 ABI is similar to the x86-64 ABI but uses 32-bit pointers. (Refer to https://sites.google.com/site/x32abi) Based on: https://github.com/libjpeg-turbo/libjpeg-turbo/pull/274/commits/8da8fc5213d87336d6c7200aaeeca925603e12cf https://github.com/libjpeg-turbo/libjpeg-turbo/pull/274/commits/1e33dfea8042230e266b453f53d69a6e37b7f0de https://github.com/libjpeg-turbo/libjpeg-turbo/pull/274/commits/24ffea78da0f18d0d467d16e02dfb903e6c0181e https://github.com/libjpeg-turbo/libjpeg-turbo/pull/274/commits/dedcf76753c8913ef5c3c6e4ea329d29494b6065 https://github.com/libjpeg-turbo/libjpeg-turbo/pull/274/commits/d04228a7b58b9aed5bcbec383630ec1a14a3c9ca https://github.com/libjpeg-turbo/libjpeg-turbo/pull/274/commits/b4ad38316ae1899c8a00b6568bb0325d82edcd7a Closes #274