Mark dex2oat_wrapper as executable.

Bazel requires srcs of a shell binary are executable, but
dex2oat_wrapper was not marked as such.

Test: presubmit
Change-Id: I773c8759af99f232909f5ca612be85af06ca4c68
diff --git a/tools/dex2oat_wrapper b/tools/dex2oat_wrapper
old mode 100644
new mode 100755