Adding switch for shmem

src/epics/util/Userspace_CMakeLists.cmake

@@ -22,6 +22,10 @@ if(${USE_STDLIB_MATH})
     list(APPEND CFLAGS "-DUSE_STDLIB_MATH=1") 
 endif()
 
+if(${DEFAULT_TO_SHMEM_BUFFERS})
+    list(APPEND CFLAGS "-DDEFAULT_TO_SHMEM_BUFFERS=1")
+endif()
+
 # Turn the ; seperated list into space seperated list and add to CFLAGS
 string(REPLACE ";" " " CFLAGS_SPACE_SEPERATED "${CFLAGS}")
 set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${CFLAGS_SPACE_SEPERATED}" )