Change priority of gen_snapshot search paths

[liamappelbe]

Description

Arm gen_snapshot has moved from clang_x86 to clang_x64 as of flutter/engine#10010. This causes a problem for people upgrading from older versions of flutter, because they will still have the old gen_snapshot in the clang_x86 directory in their artifacts cache.

We can't delete the clang_x86 directory from the list of searched directories, because we still build x86 targeting gen_snapshot as an x86 binary. So as a hacky fix I've changed the order of the directories so that we search for clang_x64 before falling back to clang_x86. This should handle the upgrade case.

Related Issues

#22598

[fluttergithubbot]

It looks like this pull request may not have tests. Please make sure to add tests before merging. While there are exceptions to this rule, if this patch modifies code it is probably not an exception.

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[codecov]

Codecov Report

Merging #37647 into master will decrease coverage by 1.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #37647      +/-   ##
==========================================
- Coverage   56.24%      55%   -1.24%     
==========================================
  Files         193      193              
  Lines       18143    18015     -128     
==========================================
- Hits        10204     9910     -294     
- Misses       7939     8105     +166

Flag	Coverage Δ
#flutter_tool	55% <ø> (-1.24%)	⬇️

Impacted Files	Coverage Δ
packages/flutter_tools/lib/src/artifacts.dart	68.08% <ø> (ø)	⬆️
...s/flutter_tools/lib/src/windows/visual_studio.dart	2.17% <0%> (-80.44%)	⬇️
...ges/flutter_tools/lib/src/resident_web_runner.dart	7.04% <0%> (-62.56%)	⬇️
...s/flutter_tools/lib/src/test/flutter_platform.dart	0.53% <0%> (-27.88%)	⬇️
packages/flutter_tools/lib/src/run_cold.dart	10.38% <0%> (-9.37%)	⬇️
packages/flutter_tools/lib/src/android/gradle.dart	42.6% <0%> (-2.46%)	⬇️
packages/flutter_tools/lib/src/web/web_device.dart	49.01% <0%> (-1.97%)	⬇️
packages/flutter_tools/lib/src/version.dart	90.73% <0%> (-1.96%)	⬇️
packages/flutter_tools/lib/src/web/chrome.dart	7.46% <0%> (-1.5%)	⬇️
packages/flutter_tools/lib/src/macos/xcode.dart	52.72% <0%> (-0.85%)	⬇️
... and 16 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 500d7c5...0d78fc9. Read the comment docs.

[cbracken]