cmake: install the config header file properly
cmake: install the config header file properly

Without specifying that the header is in the current binary directory, cmake
assumes that the file is in the source directory.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc