libgccjit: Fix UB in gcc_jit_context_new_array_constructor #536

Job	Run time
build (ubuntu-24.04, amd64, false, gcc-15)	31m 9s
build (ubuntu-24.04-arm, -aarch64, arm64, true, gcc-15-without-int128)	26m 33s
build (ubuntu-24.04-arm, -aarch64, arm64, false, gcc-15)	26m 16s
build (ubuntu-24.04, amd64, true, gcc-15-without-int128)	50m 44s
	2h 14m 42s

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