fixit: Make most tools/ work on Windows

- Turn run_buildtools_binary into a python script
  so it can be used on windows as well.
- Make tools/gen_all skip gen_{android,bazel}
  as it's too hard to make those generator work
  due to the different GN config (The rest works)
- Minor fix for \\ vs // and other small Windows-related
  issues.

Bug: 181047869
Test: python3 tools/gen_all out\win

Change-Id: I55ed1969a76cb35f1d94c849f24519aa9ac13010

tools/check_proto_comments

diff --git a/tools/check_proto_comments b/tools/check_proto_comments
index 6e7392f..74b584b 100755
--- a/tools/check_proto_comments
+++ b/tools/check_proto_comments
@@ -35,7 +35,7 @@
         continue
       if not fpath.endswith('.proto'):
         continue
-      with open(fpath) as f:
+      with open(fpath, encoding='UTF-8') as f:
         lines = f.readlines()
       for line in lines:
         comm = line.find('//')