[dovecot/core] 33c052: lib/bits.h: Fix compiling with gcc 3.0 .. 3.3

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/dovecot/core
  Commit: 33c05298ab11c13b409da265a6bf2f745196156f
      https://github.com/dovecot/core/commit/33c05298ab11c13b409da265a6bf2f745196156f
  Author: Timo Sirainen <timo.sirainen at dovecot.fi>
  Date:   2017-06-21 (Wed, 21 Jun 2017)

  Changed paths:
    M src/lib/bits.h

  Log Message:
  -----------
  lib/bits.h: Fix compiling with gcc 3.0 .. 3.3

According to gcc's online manuals, 3.4 is the first version with
__builtin_clzll