Replace exec_program with execute_process for qmake queries.

Modules/FindQt4.cmake

@@ -447,7 +447,10 @@ MACRO (_QT4_ADJUST_LIB_VARS _camelCaseBasename)
 ENDMACRO (_QT4_ADJUST_LIB_VARS)
 
 function(_QT4_QUERY_QMAKE VAR RESULT)
-  exec_program(${QT_QMAKE_EXECUTABLE} ARGS "-query ${VAR}" RETURN_VALUE return_code OUTPUT_VARIABLE output )
+  execute_process(COMMAND "${QT_QMAKE_EXECUTABLE}" -query ${VAR}
+    RESULT_VARIABLE return_code
+    OUTPUT_VARIABLE output ERROR_VARIABLE output
+    OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_STRIP_TRAILING_WHITESPACE)
   if(NOT return_code)
     file(TO_CMAKE_PATH "${output}" output)
     set(${RESULT} ${output} PARENT_SCOPE)