Restoring a line from the older version (GYP-days) of the
build_ios_libs.sh script: modifying PATH so that the
PlistBuddy utility can be successfully found and called,
as it normally is not available under the PATH directories
in a typical OS X environment (even on developer configs).
NOTRY=True
BUG=webrtc:6372
Review-Url: https://codereview.webrtc.org/2463623002
Cr-Commit-Position: refs/heads/master@{#14834}
18b8774792