Add 64-bit flag on INTERFACE64 only

Author: felixonmars

cmake/fc.cmake

@@ -65,7 +65,9 @@ if (${F_COMPILER} STREQUAL "GFORTRAN" OR ${F_COMPILER} STREQUAL "F95")
     endif ()
     if (RISCV64)
       if (BINARY64)
-        set(FCOMMON_OPT "${FCOMMON_OPT} -fdefault-integer-8")
+        if (INTERFACE64)
+          set(FCOMMON_OPT "${FCOMMON_OPT} -fdefault-integer-8")
+        endif ()
       endif ()
     endif ()
   else ()