FindFLEX: fix version parsing when the executable is quoted

Modules/FindFLEX.cmake

@@ -94,7 +94,7 @@ IF(FLEX_EXECUTABLE)
     # older versions of flex printed "/full/path/to/executable version X.Y"
     # newer versions use "basename(executable) X.Y"
     GET_FILENAME_COMPONENT(FLEX_EXE_NAME "${FLEX_EXECUTABLE}" NAME)
-    STRING(REGEX REPLACE "^.*${FLEX_EXE_NAME} (version )?([0-9]+[^ ]*)$" "\\2"
+    STRING(REGEX REPLACE "^.*${FLEX_EXE_NAME}\"? (version )?([0-9]+[^ ]*)$" "\\2"
       FLEX_VERSION "${FLEX_version_output}")
     UNSET(FLEX_EXE_NAME)
   ENDIF()