benchmark: drop all bm_ prefix for legacy driver.rb

benchmark/*.rb is only benchmarks now. We don't need prefixes.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63928 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

benchmark/io_file_write.rb

@@ -0,0 +1,14 @@
+#
+# Seek and Write file.
+#
+
+require 'tempfile'
+
+max = 200_000
+str = "Hello world!  " * 1000
+f = Tempfile.new('yarv-benchmark')
+
+max.times{
+  f.seek 0
+  f.write str
+}