In Civilization V does a workshop help build wonders?

The workshop says that it adds +20% production when constructing buildings. Are wonders considered buildings?

No. Workshops do not help wonders.

On the city screen, production is listed in the top left corner. You can see how production is calculated by mousing over the listing.

So I did a simple test. I found a city with a workshop, and looked at production while working on a building. It clearly listed "Modifier for buildings: 20%". I changed the city to working on a wonder, and that modifier disappeared, and production dropped appropriately.

Since version 1.0.1.217 (1st March 2011) the workshop now does help with the construction of wonders.

As per the patch notes:

Workshop provides 2 production (bonus reduced to +15% but affects ALL production); cost increased

I wondered this, since The Pyramids, Pentagon etc. are buildings in real life. However The Pyramids isn't a Building in Civ 5 - it's a Wonder. This difference is indicated when you choose what you are going to build next: the options are grouped into Units, Buildings, Wonders, and Other. (But workshops are still really useful imo.)