Allow overriding script executable in .gn file

This eliminates the need for using gn executable wrapper in cases
where a custom script interpreter is always being used.

Review-Url: https://codereview.chromium.org/2936773006
Cr-Original-Commit-Position: refs/heads/master@{#481105}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a104997ecbfd50c1d6a3399a49c9ad52c198259c
3 files changed
tree: 9d3d2fd806da9419b6d8d4018aa23261ff4e66a3
  1. tools/