extend/ENV/super: always set PKG_CONFIG_LIBDIR

[cho-m]

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Setting PKG_CONFIG_LIBDIR overrides compiled default. This helps reduce opportunistic linkage when pkg-config call finds modules installed on system but not included in a formula's dependency tree.

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The default on Linux is:

• #{HOMEBREW_PREFIX}/lib/pkgconfig
• #{HOMEBREW_PREFIX}/share/pkgconfig
• #{HOMEBREW_LIBRARY}/Homebrew/os/linux/pkgconfig

Removing first 2 are needed to avoid opportunistic linkage. The final path doesn't exist.

On macOS, PKG_CONFIG_LIBDIR is:

brew/Library/Homebrew/extend/os/mac/extend/ENV/super.rb

Line 29 in e9b0285

[Pathname("/usr/lib/pkgconfig"), Pathname("#{HOMEBREW_LIBRARY}/Homebrew/os/mac/pkgconfig/#{MacOS.version}")]

[cho-m]

Need to try some formulae out to see any issues.

Currently saw openjdk having trouble finding harfbuzz but not sure why as it is a dependency so should be on PKG_CONFIG_PATH.

EDIT: openjdk was local issue as I am testing on ARM Linux so building everything from source. Specifically freetype had opportunistic linkage. Rebuilding freetype with this PR fixed pkg-config to only use formula dependencies.

[MikeMcQuaid]

Makes sense to me!