[gametracer] Add v0.2.1

[mnshkw]

New package: gametracer v0.2.1

Adds a BinaryBuilder recipe for gametracer,
a C++ game-theory solver library providing the IPA and GNM algorithms.

Architecture

This JLL is part of a larger integration pipeline:

C++ (QuantEcon/gametracer) → C ABI shim (c_api/) → gametracer_jll → GameTracer.jl ← GameTheory.jl

• gametracer_jll ships libgametracer (this package).
• GameTracer.jl depends on gametracer_jll and GameTheory.jl
  (for NormalFormGame inputs), and exposes the user-facing
  ipa_solve / gnm_solve API.
• GameTheory.jl does not depend on GameTracer.jl
  (solver backend is an opt-in add-on).

What this recipe builds

• Source: QuantEcon/gametracer pinned to commit
  49ba14e
  (merge commit of c_api → main; tag v0.2.1 planned)
• Build entrypoint: cmake -S c_api -B build
  (builds the C ABI shim only; does not build the gt CLI)
• Product: LibraryProduct("libgametracer", :libgametracer) only
  • No ExecutableProduct for gt
• Exported C symbols: ipa, gnm, gametracer_free
• Install layout:
  • Library → ${libdir}/libgametracer.${dlext}
  • License → ${prefix}/share/licenses/gametracer/COPYING

Changes from the previous draft (PR #13155)

Item	Previous (PR #13155)	This PR
GIT_SHA	12aa4bb... (stale c_api branch HEAD)	49ba14e... (correct merge commit)
SHA declaration	inline inside GitSource(...)	const GIT_SHA = "..." at top of file
set -euxo pipefail	absent	added
test -d c_api / test -f c_api/CMakeLists.txt	absent	added
Post-install check: libgametracer.${dlext}	absent	added
Post-install check: COPYING	absent	added
Shell variable quoting	unquoted ${prefix} etc.	quoted "${prefix}" etc.
preferred_gcc_version=v"8"	present	removed (CMakeLists.txt sets CXX_STANDARD 11 explicitly)
supported_platforms(experimental=true)	present	removed (deferred to follow-up PR after first CI pass)

Notes

• c_api/CMakeLists.txt sets CMAKE_CXX_STANDARD 11 and CMAKE_CXX_EXTENSIONS ON
  explicitly, so no preferred_gcc_version pin is required.
• The build script performs sanity checks before CMake runs (source layout)
  and post-install checks (shared library, license file) to catch failures early.
• Experimental platforms deferred; can be added in a follow-up PR once CI
  passes on the stable platform set.

Checklist

• build_tarballs.jl uses set -euxo pipefail
• All shell variables are quoted
• LibraryProduct only (no ExecutableProduct)
• License file verified in build script
• julia_compat = "1.6"
• No preferred_gcc_version pin (not required for this package)