add SDL2, SDL2_mixer and sdl2-doom #49

Job	Run time
Feeds Package Test Build / Test aarch64_generic	22m 41s
Feeds Package Test Build / Test arm_cortex-a15_neon-vfpv4	22m 47s
Feeds Package Test Build / Test arm_cortex-a9_vfpv3-d16	22m 5s
Feeds Package Test Build / Test i386_pentium-mmx	22m 42s
Feeds Package Test Build / Test mips_24kc	22m 11s
Feeds Package Test Build / Test mipsel_24kc	22m 49s
Feeds Package Test Build / Test powerpc_464fp	21m 20s
Feeds Package Test Build / Test powerpc_8548	22m 17s
Feeds Package Test Build / Test riscv64_riscv64	22m 14s
Feeds Package Test Build / Test x86_64	22m 20s
	3h 43m 26s

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