[NFC] Restructure linkage name printing in AsmWriter

This restructuring was suggested in the review for D46699, which
prepares the linkage type printer for use in printing the ThinLTO
summary index (where we want to print "external" and also don't
want a space after the linkage type as it is printed by the caller).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333281 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed