[SPEC] Use llvm_test_library instead of add_library for the cam4_netcdf target of 527.cam4_r

Similar to #238.

Author: SixWeining

External/SPEC/CFP2017rate/527.cam4_r/CMakeLists.txt

@@ -55,7 +55,7 @@ if (NOT TARGET cam4_netcdf)
     "${SRC_DIR}/spec_qsort/spec_qsort.c")
   list(REMOVE_ITEM netcdf_sources "${SRC_DIR}/netcdf/ncio.c")
 
-  add_library(cam4_netcdf OBJECT ${netcdf_sources})
+  llvm_test_library(cam4_netcdf OBJECT ${netcdf_sources})
   target_compile_definitions(cam4_netcdf PRIVATE SPEC)
 endif ()