Question: What manuscript survived the medieval Welsh poem consisting of a series of elegies to the men of the Brittonic kingdom of Godddin,  who fought a battle around AD 600 between a force raised by the Gododdin, a Brythonic people of the "Hen Ogledd" or "Old North" of Britain, and the Angles of Bernicia and Deira?
Context: Rhydderch Hael (Welsh: "Rhydderch the Generous" , fl.  580 – c. 614) was a ruler of Alt Clut, a Brittonic kingdom in the "Hen Ogledd" or "Old North" of Britain.  He was one of the most famous kings in the "Hen Ogledd", and appears frequently in later medieval works in Welsh and Latin. Yr Hen Ogledd (] ), in English the Old North, is the region of Northern England and the southern Scottish Lowlands inhabited by the Celtic Britons of sub-Roman Britain and the Early Middle Ages.  Its denizens spoke a variety of the Brittonic language known as Cumbric.  The Hen Ogledd was distinct from the parts of northern Britain inhabited by the Picts, Anglo-Saxons, and Scoti as well as from Wales, although the people of the Hen Ogledd were the same Brittonic stock as the Picts, Welsh and Cornish, and the region loomed large in Welsh literature and tradition for centuries after its kingdoms had disappeared. Clinoch (Welsh: "Clynog" ) is thought to have been a ruler of Alt Clut, the Brittonic kingdom later known as Strathclyde, some time in the 6th century.  The Harleian genealogies name Clinoch as the son of Dumnagual Hen, his probable predecessor as King of Alt Clut, and the father of Tutagual, his probable successor.  The "Bonedd Gwŷr y Gogledd", a later genealogy of rulers in the "Hen Ogledd" or "Old North" of Britain, names the descendant between Dumnagual and Tutagual Kedic. The Gododdin (] ) were a P-Celtic speaking Brittonic people of north-eastern Britannia, the area known as the Hen Ogledd or Old North (modern south-east Scotland and north-east England), in the sub-Roman period.  Descendants of the Votadini, they are best known as the subject of the 6th-century Welsh poem "Y Gododdin", which memorialises the Battle of Catraeth and is attributed to Aneirin. Cinuit (Welsh: "Cynwyd" ) may have been an early ruler of the Brittonic kingdom of Alt Clut, later known as Strathclyde, in Britain's "Hen Ogledd" or "Old North".  The Harleian genealogies indicate that he was the son of Ceretic Guletic, who may be identified with the warlord "Ceredig" rebuked by Saint Patrick in one of his letters.  According to the same pedigrees, he was the father of Dumnagual Hen, an important but obscure ancestor figure in Welsh tradition.  The later genealogy "Bonedd Gwŷr y Gogledd" replaces Cinuit as Dumnagual's father with a certain Idnyuet, said to be the son of Maxen Wledic (the Roman usurper Magnus Maximus).  However, the "Bonedd" does include a "Cynwyd Cynwydion" in the ancestry of Clydno Eiddyn, and a Triad attached to the text mentions the "three hundred swords of the (tribe of) Cynwydion" as one of three formidable north British war bands, along with those of Coel Hen and Cynfarch. The Battle of Catraeth was fought around AD 600 between a force raised by the Gododdin, a Brythonic people of the "Hen Ogledd" or "Old North" of Britain, and the Angles of Bernicia and Deira.  It was evidently an assault by the Gododdin party on the Angle stronghold of Catraeth, perhaps Catterick, North Yorkshire.  The Gododdin force was said to have consisted of warriors from all over the Hen Ogledd, and even some from as far afield as Gwynedd in North Wales and Pictland.  The battle was disastrous for the Britons, who were nearly all killed.  The slain warriors were commemorated in the important early poem "Y Gododdin", attributed to Aneirin. Tutagual (Welsh: "Tudwal" ) is thought to have been a ruler of Alt Clut, later known as Strathclyde, a Brittonic kingdom in the "Hen Ogledd" or "Old North" of Britain.  He probably ruled sometime in the mid-6th century. Y Gododdin (] ) is a medieval Welsh poem consisting of a series of elegies to the men of the Brittonic kingdom of Gododdin and its allies who, according to the conventional interpretation, died fighting the Angles of Deira and Bernicia at a place named "Catraeth" in c. AD 600.  It is traditionally ascribed to the bard Aneirin and survives only in one manuscript, the Book of Aneirin. Mynyddog Mwynfawr (variant orthographies include: Old Welsh "Mynydawc Mwynvawr"; Middle Welsh; "Mynyddawg Mwynfawr") was, according to Welsh tradition founded on the early Welsh language poem "Y Gododdin" (attributed to Aneirin), a Brittonic ruler of the kingdom of Gododdin in the Hen Ogledd (southern Scotland). Dyfnwal Hen or Dumnagual Hen ("Dyfnwal the Old") was a ruler of the Brittonic kingdom of Alt Clut, later known as Strathclyde, probably sometime in the early 6th century.  His biography is vague, but he was regarded as an important ancestor figure for several kingly lines in the "Hen Ogledd" or "Old North" of Britain.  As an ancestor figure, he compares to Coel Hen, another obscure figure credited with founding a number of northern dynasties.
Answer: Book of Aneirin