Third-party: Disable -Werror for flatcc build #5030

Job	Run time
test-vulkan / test-backend-linux (vulkan, operators) / linux-job	21m 9s
test-vulkan / test-backend-linux (vulkan, models) / linux-job	21m 1s
test-vulkan / test-backend-macos	-1s
test-vulkan / package-golden-artifacts	3m 33s
	45m 42s

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