The beauty of the LDS doctrine is it can be changed as needed. With the new marketing efforts of the past couple of decades you will struggle to find any mention of this now, at least publicly. In trying to market being "Christan" now, efforts at changing their overall history and the words of their forefathers have be moving along at a brisk pace. Seems all those "odd" ideas are a stumbling block in recruitment now.
As far as the Virgin Mary subject, it is the same as trying to nail them down on how many gods they believe in. Jello does not nail very well.
Indeed at one point in searching the actual links to the Journals and Discourses and such I found pages missing on the subject at LDS web sources. No surprise there.
However God will provide...
“The birth of the Saviour was as natural as are the births of our children; it was the result of natural action. He partook of flesh and blood—was begotten of his Father, as we were of our fathers,” (Journal of Discourses, v. 8, p. 115).
“The birth of the Savior was a natural occurrence unattended with any degree of mysticism, and the Father God was the literal parent of Jesus in the flesh as well as in the spirit,” (Religious Truths Defined, p. 44, as cited in the book, Mormonism: Shadow or Reality, by Gerald and Sandra Tanner, Utah Lighthouse Ministry, P.O. Box 1854, Salt Lake City, Utah 84110, bookstore at 1350 South West Temple, 1982, p. 260).
“The man Joseph, the husband of Mary, did not, that we know of, have more than one wife, but Mary the wife of Joseph had another husband,” (Deseret News, October 10, 1866, as cited in the book, Mormonism: Shadow or Reality, by Gerald and Sandra Tanner, Utah Lighthouse Ministry, P.O. Box 1854, Salt Lake City, Utah 84110, bookstore at 1350 South West Temple, 1982, p. 261).
Mormon apostle Bruce McConkie, in perhaps the most explicit denial of the virgin birth, wrote,
“Christ was Begotten by an immortal Father in the same way that mortal men are begotten by mortal fathers.” (Mormon Doctrine, 1966, p. 547)
You might ask, “How can Mormons who believe this say that Christ was born of a virgin?” This is done by changing the definition of the word “virgin”. The virgin Mary did not have sexual relations with a mortal man, they say, but instead was impregnated by an immortal man. Bruce McConkie wrote,
“Our Lord is the only mortal person ever born to a virgin, because he is the only person who ever had an immortal Father.” (Mormon Doctrine, 2nd ed., p. 822)
Moving goal posts is a very time honored LDS practice. Hard to be wrong when whatever you say is “right” and your detractors can't hit a moving target, at least for a few minutes.
Other sources:
http://www.mrm.org/virgin-birth
http://www.exmormon.org/mormon/mormon385.htm
http://www.carm.org/religious-movements/mormonism/was-lds-jesus-born-virgin-mary
Just like greek mythology