ישבתי [יֹשַׁבְתְּ֙] בַּלְּבָנ֔וֹן מקננתי [מְקֻנַּ֖נְתְּ] בָּֽאֲרָזִ֑ים מַה־נֵּחַנְתְּ֙ בְּבֹא־לָ֣ךְ חֲבָלִ֔ים חִ֖יל כַּיֹּלֵדָֽה׃
O toi, qui demeures sur le Liban, qui fixes ton nid sur les cèdres, comme tu seras un objet de pitié, lorsque des douleurs viendront t’assaillir, des convulsions comparables à celles d’une femme en travail!
Rashi
וְיֹלַדְתְּ בן AND THOU SHALT BEAR A SON — The word appears to be grammatically a combination of the perfect tense וְיָלַדְתְּ and the participle וְיֹלֶדֶת but it is similar in sense to וְיֹלֶדֶת (the participle); so, also, (Jeremiah 22:23) “O thou that dwellest יֹשַׁבְתְּ) in Lebanon, and art nestled (מְקֻנַּנְתְּ) in the cedars.”
Siftei Chakhamim
As if it were written ויולדת... I.e., יוֹלֶדֶת, which is present tense. [Rashi is saying:] Do not be surprised by the שוא under the ת, for it is similar to (Yirmeyahu 22:23):יושבת בלבנון מקוננת בארזים, which also are present tense, and have a שוא under the ת.