cmake MPREAL examples

timi-liuliang/echo thirdparty/google/eigen/unsupported/test/CMakeLists.txt :54 

find_package(MPREAL)

IBAMR/IBAMR ibtk/contrib/eigen/unsupported/test/CMakeLists.txt :58 

find_package(MPREAL)

chsl/PLADE code/3rd_party/eigen-3.4.0/unsupported/test/CMakeLists.txt :58 

find_package(MPREAL)