gtk-vnc: add indirect dependencies

[iMichka]

Fixes:
Full linkage --cached --test --strict gtk-vnc output
Indirect dependencies with linkage:
at-spi2-core
harfbuzz
libx11
pango

I took the opportunity to move the gettext build dep to the on_linux block:

• it's a build time dep on Linux
• it's a normal dep on macOS

• Have you followed the guidelines for contributing?
• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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[chenrui333]

no linkage for this?

[chenrui333]

this should be linux dep only?

[cho-m]

As note, linkage failures on Ventura/Sonoma bottles can be incorrect for meson-based formulae if they haven't been rebuilt recently.

Usually need to verify Monterey/Sequoia bottles, which never used buggy Xcode 15 linker.

Otherwise will end up incorrectly adding dependencies. If want to get rid of warning, then need new bottles.

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EDIT: Specifically, this is due to meson's default usage of -dead_strip_dylibs/--as-needed which was broken on some Xcode 15 releases when using new linker. brew has a workaround to use -ld_classic for buggy Xcode versions.

[carlocab]

This is also a macOS dependency (see on_macos block above), so we can make the :build dependency unconditional