Reland of Enable -Wunused-lambda-capture warning (patchset #1 id:1 of https://codereview.webrtc.org/3007483002/ )

Reason for revert:
Relanding not enabling the warning if Xcode clang is used.
See https://cs.chromium.org/chromium/src/build/config/compiler/BUILD.gn?rcl=9de57af4acd3e74cde57e62dd48e58290eeb1481&l=1216
for details.

Original issue's description:
> Revert of Enable -Wunused-lambda-capture warning (patchset #1 id:1 of https://codereview.webrtc.org/2999403002/ )
>
> Reason for revert:
> Breaks iOS framework builder.
>
> Original issue's description:
> > Enable -Wunused-lambda-capture warning
> >
> > This should prevent some build errors downstream.
> > The warning is currrently disabled in Chromium:
> > https://cs.chromium.org/chromium/src/build/config/compiler/BUILD.gn?rcl=735aa36217a394455f70aad87e2c844053fd810a&l=1214
> > (see https://crbug.com/681136 for more info).
> >
> > BUG=webrtc:7133
> > NOTRY=True
> >
> > Review-Url: https://codereview.webrtc.org/2999403002
> > Cr-Commit-Position: refs/heads/master@{#19466}
> > Committed: https://chromium.googlesource.com/external/webrtc/+/fd7cffa43366d5fb8a95da71fffa7f872037fefe
>
> TBR=charujain@webrtc.org,charujain@google.com
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=webrtc:7133
>
> Review-Url: https://codereview.webrtc.org/3007483002
> Cr-Commit-Position: refs/heads/master@{#19473}
> Committed: https://chromium.googlesource.com/external/webrtc/+/aa0d2e694a965c72b5adc0c7779b81e850db46e6

TBR=charujain@webrtc.org,charujain@google.com
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:7133

Review-Url: https://codereview.webrtc.org/3002203002
Cr-Original-Commit-Position: refs/heads/master@{#19475}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d4ab933e2c6142e0d398b0afd30626b476f7082f
1 file changed