duplicated macro 'with-storage'

[fraya]

This macro is defined in:

• opendylan/sources/common-dylan/timers.dylan

  Line 47 in 45f46ba

  define macro with-storage

• opendylan/sources/system/unix-operating-system.dylan

  Line 10 in 45f46ba

  define macro with-storage

@cgay comment in chat that it should be exported from common-dylan and documented.

[housel]

See also with-stack-structure in the C-FFI library.