cmd/link, cmd/internal/dwarf: add DWARF5 line table support
This patch rolls out the necessary changes to migrate the DWARF line
table support in the compiler and linker to DWARF version 5, gated by
the "dwarf5" GOEXPERIMENT.
DWARF version 5 includes a number of changes to the line table,
notably a revamped prolog section and a change in the indexing system
used to refer to files and directories within the line table
program. Specifically, prior to DWARF 4 a compilation's directory
table was considered to have an implicit zero entry containing the
compilation directory of the translation unit (package), and the file
table was considered to have an implicit zero entry storing the
"primary source file" (stored in the compilation unit DIE name).
DWARF 5 does away with these implicity entries meaning that files and
dirs are now effectively a 0-based index.
Updates #26379.
Change-Id: I9b4f1be5415aacec1ba57366d60bd48819c56ea5
Reviewed-on: https://go-review.googlesource.com/c/go/+/633879 Reviewed-by: Alessandro Arzilli <alessandro.arzilli@gmail.com> Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com>