Ignore genperf lib in merge_libs.py.

It's built as a part of the chromium build(?), but causes problems with XCode 7's new bitcode intermediate format. It should really never been included, but it never caused link failures before.

BUG=

Review URL: https://codereview.webrtc.org/1236383002

Cr-Commit-Position: refs/heads/master@{#9606}
diff --git a/webrtc/build/merge_libs.py b/webrtc/build/merge_libs.py
index f020594..066e3ab 100644
--- a/webrtc/build/merge_libs.py
+++ b/webrtc/build/merge_libs.py
@@ -16,7 +16,7 @@
 import subprocess
 import sys
 
-IGNORE_PATTERNS = ['do_not_use', 'protoc']
+IGNORE_PATTERNS = ['do_not_use', 'protoc', 'genperf']
 
 def FindFiles(path, pattern):
   """Finds files matching |pattern| under |path|.