add another llvm bug

found with the new over-abstraction implementation :D

BugList.md

@@ -53,6 +53,7 @@ Please contact us or submit a PR if something is missing or inaccurate.
 46. Loop peeling introduces OOB stores (https://llvm.org/PR48125)
 47. Loop vectorizer introduces gep inbounds with negative offset (https://llvm.org/PR48126)
 48. DSE incorrectly removes store in function that only triggers UB in one of the branches (https://llvm.org/PR48521)
+49. Incorrect swap of fptrunc with fast-math instructions (https://llvm.org/PR49080)
 
 
 ### Bugs found in Z3