add pffft

pffft/cmake/FindMIPP.cmake

@@ -0,0 +1,26 @@
+
+if(MIPP_INCLUDE_DIRS)
+  set(MIPP_FIND_QUIETLY TRUE)
+endif()
+
+find_path(MIPP_INCLUDE_DIRS NAMES mipp.h
+    HINTS
+        ${MIPP_ROOT}
+        $ENV{HOME}/.local
+    PATH_SUFFIXES include/mipp
+)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(MIPP DEFAULT_MSG MIPP_INCLUDE_DIRS)
+
+if(MIPP_FOUND AND NOT TARGET MIPP)
+    message(STATUS "MIPP_FOUND -> creating interface library MIPP at ${MIPP_INCLUDE_DIRS}")
+    add_library(MIPP INTERFACE)
+    target_compile_definitions(MIPP INTERFACE HAVE_MIPP=1)
+    target_include_directories(MIPP INTERFACE ${MIPP_INCLUDE_DIRS})
+    target_compile_features(MIPP INTERFACE cxx_std_11)
+else()
+    message(WARNING "MIPP not found.")
+endif()
+
+mark_as_advanced(MIPP_INCLUDE_DIRS)