benchmark: Measure allocation time for objects

A basic measurement, how fast can we create and populate an object with
backing storage?

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/benchmarks/.gitignore b/benchmarks/.gitignore
index 7964d86..f5e55aa 100644
--- a/benchmarks/.gitignore
+++ b/benchmarks/.gitignore
@@ -1,3 +1,4 @@
+gem_create
 gem_exec_ctx
 gem_exec_nop
 gem_mmap