CMake/FindBoost: Fix policy CMP0054 warning (added in 3.1)

(cherry picked from commit 7e6dadfea68836cc92aaa7e1bb770be620225aa2)

cmake/macros/FindBoost.cmake

@@ -341,9 +341,9 @@ endfunction()
 # Guesses Boost's compiler prefix used in built library names
 # Returns the guess by setting the variable pointed to by _ret
 function(_Boost_GUESS_COMPILER_PREFIX _ret)
-  if("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Intel"
-      OR "${CMAKE_CXX_COMPILER}" MATCHES "icl"
-      OR "${CMAKE_CXX_COMPILER}" MATCHES "icpc")
+  if(${CMAKE_CXX_COMPILER_ID} STREQUAL "Intel"
+      OR ${CMAKE_CXX_COMPILER} MATCHES "icl"
+      OR ${CMAKE_CXX_COMPILER} MATCHES "icpc")
     if(WIN32)
       set (_boost_COMPILER "-iw")
     else()