Fallback to VCS.release_date on VCS::NotFoundError

when -q is given.

One of the RubyCI servers, freebsd12, had a broken git environment:

```
$ git show
fatal: detected dubious ownership in repository at '/usr/home/chkbuild/chkbuild/tmp/build/20220917T123002Z/ruby'
To add an exception for this directory, call:

        git config --global --add safe.directory /usr/home/chkbuild/chkbuild/tmp/build/20220917T123002Z/ruby
```

tool/lib/vcs.rb doesn't work normally for that server.
Even for such cases, we'd like to generate a usable revision.h.

So this patch lets revision.h fallback to default VCS.release_date
when VCS::NotFoundError is raised.

tool/file2lastrev.rb

@@ -68,13 +68,11 @@ OptionParser.new {|opts|
 }
 unless vcs
   # Output only release_date when .git is missing
-  if @output == :revision_h
+  puts VCS.release_date if @output == :revision_h
-    puts VCS.release_date(Time.now - 10) # same as make-snapshot
-  end
   exit
 end
 
-@output =
+output =
   case @output
   when :changed, nil
     Proc.new {|last, changed|
@@ -99,9 +97,12 @@ end
 ok = true
 (ARGV.empty? ? [nil] : ARGV).each do |arg|
   begin
-    puts @output[*vcs.get_revisions(arg)]
+    puts output[*vcs.get_revisions(arg)]
   rescue => e
-    next if @suppress_not_found and VCS::NotFoundError === e
+    if @suppress_not_found and VCS::NotFoundError === e
+      puts VCS.release_date if @output == :revision_h
+      next
+    end
     warn "#{File.basename(Program)}: #{e.message}"
     ok = false
   end

tool/lib/vcs.rb

@@ -95,7 +95,7 @@ class VCS
     opts
   end
 
-  def self.release_date(time)
+  def self.release_date(time = Time.now - 10) # the same default as make-snapshot
     t = time.utc
     [
       t.strftime('#define RUBY_RELEASE_YEAR %Y'),