Don't emit STB_UNIQUE symbols in GCC for vortex-duckdb #5842

Job	Run time
C++ API (coverage)	1m 8s
Rust tests (tsan)	6m 1s
Rust/C++ FFI tests (tsan)	1m 55s
Rust tests (asan)	6m 42s
Rust tests (miri)	1m 35s
Rust/C++ FFI tests (asan)	2m 10s
Mirror DuckDB to R2 / Resolve DuckDB version and check R2	5s
DuckDB libraries available in R2	2s
Mirror DuckDB to R2 / Mirror DuckDB ${{ matrix.archive }} to R2	0s
Rust tests (coverage) (tests)	5m 51s
	25m 29s

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