gold speed for small programs

[Ralf Wildenhues]

Trying out gold (no LTO) on GCC's cc1, a log shows that the single
biggest part (20%) of user time for such a medium sized program may be
spent in SHA1 computation for the build id.  I think the SHA1 code in
libiberty would benefit from an SSE implementation, such as the one
found in git or described on <http://en.wikipedia.org/wiki/SHA-1>.

Adding bug-gnulib in Cc: because that's where the libiberty SHA1
implementation comes from.

Cheers,
Ralf