Enable sparse_sort_crs perf test based on CMake var

Instead of just commenting out the cmake.
-DKokkosKernels_ENABLE_SORT_CRS_PERFTEST=ON will enable it (off by
default)

perf_test/sparse/CMakeLists.txt

@@ -116,12 +116,14 @@ KOKKOSKERNELS_ADD_EXECUTABLE(
         SOURCES KokkosSparse_mdf.cpp
 )
 
-# Do not build this CRS sorting perf test by default.
-# It can be enabled if needed by uncommenting these lines.
-#KOKKOSKERNELS_ADD_EXECUTABLE(
-#        sparse_sort_crs
-#        SOURCES KokkosSparse_sort_crs.cpp
-#)
+# For the sake of build times, don't build this CRS sorting perf test by default.
+# It can be enabled if needed by setting -DKokkosKernels_ENABLE_SORT_CRS_PERFTEST=ON.
+if (KokkosKernels_ENABLE_SORT_CRS_PERFTEST)
+  KOKKOSKERNELS_ADD_EXECUTABLE(
+    sparse_sort_crs
+    SOURCES KokkosSparse_sort_crs.cpp
+)
+endif ()
 
 if (KokkosKernels_ENABLE_BENCHMARK)
   KOKKOSKERNELS_ADD_BENCHMARK(