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/vm_thread_mutex2.rb

@@ -0,0 +1,21 @@
+# two threads, one mutex
+
+require 'thread'
+m = Thread::Mutex.new
+r = 0
+max = 2000
+lmax = (max * max)/2
+(1..2).map{
+  Thread.new{
+    i = 0
+    while i<lmax
+      i += 1
+      m.synchronize{
+        r += 1
+      }
+    end
+  }
+}.each{|e|
+  e.join
+}
+raise r.to_s if r != max * max