isConcrete assertion failure in swift linker

[mmrussell]

xcode26.0.1_swift_compiler_crash.txt

Tracked through the stack trace dump to here.

swift/lib/SIL/IR/Linker.cpp

Line 305 in b985fc9

if (ref.isAbstract())

It seems the early return check if ref.isAbstract() needs to be changed to if !ref.isConcrete()