ffmpeg7: add pixeldensity feature for retina displays

[aeiouaeiouaeiouaeiouaeiouaeiou]

Description

Backport the patch to ffmpeg7, since the ffmpeg-devel port uses v7 branch.

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.6.8 10K549 x86_64
Xcode 4.2 4C199

Verification

Have you

• followed our Commit Message Guidelines?
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• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL in commit message?
• checked your Portfile with port lint?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?

[macportsbot]

Notifying maintainers:
@barracuda156 for port ffmpeg7.
@mascguy for port ffmpeg7.

[aeiouaeiouaeiouaeiouaeiouaeiou]

@mascguy the build still fails on 10.11 machine, it might be worth increasing Clang blacklist to 900.

[mascguy]

@mascguy the build still fails on 10.11 machine, it might be worth increasing Clang blacklist to 900.

Sure, go ahead and add it to this PR.

[mascguy]

LGTM, will merge once CI completes for 13 and 14.

[mascguy]

Thank you!