builder: fix cache paths in -size=full output

This fixes long paths from the TinyGo cached GOROOT, as can be seen
here:

   code  rodata    data     bss |   flash     ram | package
------------------------------- | --------------- | -------
      0       5       0       5 |       5       5 | (padding)
    148       0       0       5 |     148       5 | (unknown)
     76       0       0       0 |      76       0 | /home/ayke/.cache/tinygo/goroot-ce8827882be9dc201bed279a631881177ae124ea064510684a3cf4bb66436e1a/src/device/arm
      4       0       0       0 |       4       0 | /home/ayke/.cache/tinygo/goroot-ce8827882be9dc201bed279a631881177ae124ea064510684a3cf4bb66436e1a/src/internal/task

They're now attributed to the correct package instead (device/arm and
internal/task).

Author: aykevl

builder/build.go

@@ -690,7 +690,7 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	for _, pkg := range lprogram.Sorted() {
 		pkg := pkg
 		for _, filename := range pkg.CFiles {
-			abspath := filepath.Join(pkg.Dir, filename)
+			abspath := filepath.Join(pkg.OriginalDir(), filename)
 			job := &compileJob{
 				description: "compile CGo file " + abspath,
 				run: func(job *compileJob) error {