[NaCl SDK] Remove create_nmf dependency on NACL_SDK_ROOT env var
create_nmf should determine the root of the SDK relative
to its own location.
The exception to this is when its run as part of the
chrome build, when it is not yet installed. In this
case we pass --no-default-libpath and --objdump to
create_nmf to remove any use of the SDK root.
This is the second attempt at landing this change.
The first one was reverted:
https://codereview.chromium.org/
737653003
CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:linux_nacl_sdk;tryserver.chromium.mac:mac_nacl_sdk
BUG=none
Review URL: https://codereview.chromium.org/
1066823003
Cr-Commit-Position: refs/heads/master@{#325511}