add a support module for MPFR C++ with basic unit testing

cmake/FindMPFR.cmake

@@ -0,0 +1,21 @@
+# Try to find the MPFR library
+# See http://www.mpfr.org/
+
+if (MPFR_INCLUDES AND MPFR_LIBRARIES)
+  set(MPFR_FIND_QUIETLY TRUE)
+endif (MPFR_INCLUDES AND MPFR_LIBRARIES)
+
+find_path(MPFR_INCLUDES
+  NAMES
+  mpfr.h
+  PATHS
+  $ENV{GMPDIR}
+  ${INCLUDE_INSTALL_DIR}
+)
+
+find_library(MPFR_LIBRARIES mpfr PATHS $ENV{GMPDIR} ${LIB_INSTALL_DIR})
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(MPFR DEFAULT_MSG
+                                  MPFR_INCLUDES MPFR_LIBRARIES)
+mark_as_advanced(MPFR_INCLUDES MPFR_LIBRARIES)