If FFTW is not found, default to not building the PME plugin.

CMakeLists.txt

@@ -398,7 +398,12 @@ ENDIF(OPENMM_BUILD_DRUDE_PLUGIN)
 
 # CPU PME plugin
 
-SET(OPENMM_BUILD_PME_PLUGIN ON CACHE BOOL "Build CPU PME plugin")
+FIND_PACKAGE(FFTW QUIET)
+IF(FFTW_FOUND)
+    SET(OPENMM_BUILD_PME_PLUGIN ON CACHE BOOL "Build CPU PME plugin")
+ELSE(FFTW_FOUND)
+    SET(OPENMM_BUILD_PME_PLUGIN OFF CACHE BOOL "Build CPU PME plugin")
+ENDIF(FFTW_FOUND)
 SET(OPENMM_BUILD_PME_PATH)
 IF(OPENMM_BUILD_PME_PLUGIN)
    SET(OPENMM_BUILD_PME_PATH ${CMAKE_CURRENT_SOURCE_DIR}/plugins/cpupme)

plugins/cpupme/CMakeLists.txt

@@ -75,7 +75,6 @@ SET_SOURCE_FILES_PROPERTIES(${SOURCE_FILES} PROPERTIES COMPILE_FLAGS "-msse4.1")
 
 
 # Include FFTW related files.
-INCLUDE(FindFFTW)
 INCLUDE_DIRECTORIES(${FFTW_INCLUDES})
 
 # Build the plugin library.