use default64 flag for Cray ftn compiler

Author: ajaypanyala

CMakeLists.txt

@@ -53,7 +53,12 @@ if(BUILD_INDEX64)
   set(LAPACKELIB "lapacke64")
   set(TMGLIB "tmglib64")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DWeirdNEC -DLAPACK_ILP64 -DHAVE_LAPACK_CONFIG_H")
-  set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -fdefault-integer-8")
+  
+  if(CMAKE_Fortran_COMPILER_ID STREQUAL "Cray")
+    set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -default64")
+  else()
+    set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -fdefault-integer-8")  
+  endif()
 else()
   set(BLASLIB "blas")
   set(CBLASLIB "cblas")