Use absolute paths in #line directives generated

Multiple .ino files in a sketch are concatenated together, adding #line
directives so error messages refer to the original filenames. However,
these directives used plain filenames, without a path. Since these
filenames end up in the debug info as-is, this complicates using a
debugger on the resulting .elf file. Using full pathnames fixes this.

This fixes arduino/Arduino#3746.

Signed-off-by: Matthijs Kooijman <[email protected]>

Author: matthijskooijman

Diff for: src/arduino.cc/builder/sketch_source_merger.go

@@ -32,7 +32,6 @@ package builder
 import (
 	"arduino.cc/builder/constants"
 	"arduino.cc/builder/types"
-	"path/filepath"
 )
 
 type SketchSourceMerger struct{}
@@ -52,7 +51,7 @@ func (s *SketchSourceMerger) Run(context map[string]interface{}) error {
 }
 
 func addPreprocLine(sketch *types.SketchFile) string {
-	source := "#line 1 \"" + filepath.Base(sketch.Name) + "\"\n"
+	source := "#line 1 \"" + sketch.Name + "\"\n"
 	source += sketch.Source
 	source += "\n"