Fix Windows pkgconfig resolution and MSVC flag translation

[quaesitor-scientiam]

Summary

• Initialize pcfiledir when parsing .pc files so ${pcfiledir} resolves correctly on Windows/vcpkg.
• Translate gcc‑style pkgconfig tokens (-I/-L/-l, including quoted groups) into MSVC flags in the MSVC build path.
• Update pkgconfig tests to include pcfiledir.

Why

V’s internal pkgconfig didn’t set pcfiledir, so ${pcfiledir} expanded to empty and vcpkg paths collapsed to S:\include/S:\lib. This broke MSVC builds (missing ft2build.h) and leaked -L/-l tokens into MSVC. The fix aligns internal pkgconfig behavior with standard pkg-config and makes MSVC robust to gcc-style flag output.

Testing

• vnew.exe -silent vlib\v\pkgconfig\pkgconfig_test.v
• Full run: vnew.exe -silent test vlib\v\ → 14 failed, 1973 passed, 24 skipped, 2011 total
  • Fixed 1 failure: vlib\v\pkgconfig\pkgconfig_test.v
  • Remaining 13 failures are sqlite-related (environment dependency)

[quaesitor-scientiam]

Fixes #26628

[chatgpt-codex-connector]

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