cmd/compile: record regabi status in DW_AT_producer

Records if regabi was enabled during compilation in the DW_AT_producer
attribute of each compile unit.
This is useful to debuggers that support the debugCall protocol.

Change-Id: I5ad2c48ebf126aeb8bfb459b53a1a5304550036a
Reviewed-on: https://go-review.googlesource.com/c/go/+/318050
Trust: Dmitri Shuralyov <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Run-TryBot: Than McIntosh <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: aarzilli

src/cmd/compile/internal/dwarfgen/dwarf.go

@@ -531,6 +531,14 @@ func RecordFlags(flags ...string) {
 		fmt.Fprintf(&cmd, " -%s=%v", f.Name, getter.Get())
 	}
 
+	// Adds flag to producer string singalling whether regabi is turned on or
+	// off.
+	// Once regabi is turned on across the board and the relative GOEXPERIMENT
+	// knobs no longer exist this code should be removed.
+	if buildcfg.Experiment.RegabiArgs {
+		cmd.Write([]byte(" regabi"))
+	}
+
 	if cmd.Len() == 0 {
 		return
 	}