build: speed up buildroot #22

Job	Run time
Build (qemu_x86_defconfig, glibc)	7m 36s
Build (qemu_x86_defconfig, uclibc)	7m 34s
Build (qemu_x86_defconfig, musl)	1s
Build (qemu_x86_64_defconfig, glibc)	7m 37s
Build (qemu_x86_64_defconfig, uclibc)	7m 48s
Build (qemu_x86_64_defconfig, musl)	7m 38s
Build (raspberrypi4_defconfig, glibc)	1s
Build (raspberrypi4_defconfig, uclibc)	1s
Build (raspberrypi4_defconfig, musl)	1s
Build (raspberrypi4_64_defconfig, glibc)	1s
Build (raspberrypi4_64_defconfig, uclibc)	1s
Build (raspberrypi4_64_defconfig, musl)	1s
Build (qemu_ppc64le_pseries_defconfig, glibc)	7m 40s
Build (qemu_ppc64le_pseries_defconfig, uclibc)	8m 25s
Build (qemu_ppc64le_pseries_defconfig, musl)	7m 33s
Build (qemu_mips32r2_malta_defconfig, glibc)	7m 39s
Build (qemu_mips32r2_malta_defconfig, uclibc)	7m 56s
Build (qemu_mips32r2_malta_defconfig, musl)	7m 41s
Build (qemu_mips64_malta_defconfig, glibc)	8m 44s
Build (qemu_mips64_malta_defconfig, uclibc)	7m 37s
Build (qemu_mips64_malta_defconfig, musl)	7m 38s
Build (qemu_riscv32_virt_defconfig, glibc)	7m 39s
Build (qemu_riscv32_virt_defconfig, uclibc)	7m 32s
Build (qemu_riscv32_virt_defconfig, musl)	7m 41s
Build (qemu_riscv64_virt_defconfig, glibc)	7m 37s
Build (qemu_riscv64_virt_defconfig, uclibc)	7m 21s
Build (qemu_riscv64_virt_defconfig, musl)	7m 31s
	2h 34m 34s

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