sysdeps,book: add demo sysdeps and porting mdbook #4230

Job	Run time
Build mlibc (x86_64, mlibc, gcc)	38s
Compile sysdeps (dripos)	2m 22s
Build mlibc (x86_64, mlibc-static, gcc)	28s
Compile sysdeps (lemon)	2m 48s
Build mlibc (x86_64, mlibc-shared, gcc)	28s
Compile sysdeps (aero)	2m 26s
Build mlibc (x86_64, mlibc-ansi-only, gcc)	31s
Compile sysdeps (ironclad)	2m 45s
Build mlibc (x86_64, mlibc-headers-only, gcc)	28s
Compile sysdeps (lyre)	2m 39s
Build mlibc (riscv64, mlibc, gcc)	1m 5s
Compile sysdeps (keyronex)	2m 49s
Build mlibc (riscv64, mlibc-static, gcc)	56s
Compile sysdeps (managarm)	3m 7s
Build mlibc (riscv64, mlibc-shared, gcc)	50s
Compile sysdeps (vinix)	2m 18s
Build mlibc (riscv64, mlibc-ansi-only, gcc)	1m 4s
Compile sysdeps (astral)	2m 26s
Build mlibc (riscv64, mlibc-headers-only, gcc)	59s
Build mlibc (aarch64, mlibc, gcc)	3m 24s
Build mlibc (aarch64, mlibc-static, gcc)	3m 20s
Build mlibc (aarch64, mlibc-shared, gcc)	3m 24s
Build mlibc (aarch64, mlibc-ansi-only, gcc)	3m 6s
Build mlibc (aarch64, mlibc-headers-only, gcc)	1m 58s
Build mlibc (x86, mlibc, gcc)	12s
Build mlibc (x86, mlibc-static, gcc)	1s
Build mlibc (x86, mlibc-shared, gcc)	1s
Build mlibc (x86, mlibc-ansi-only, gcc)	9s
Build mlibc (x86, mlibc-headers-only, gcc)	1s
Build mlibc (m68k, mlibc, gcc)	3m 23s
Build mlibc (m68k, mlibc-static, gcc)	1m 19s
Build mlibc (m68k, mlibc-shared, gcc)	3m 0s
Build mlibc (m68k, mlibc-ansi-only, gcc)	2m 48s
Build mlibc (m68k, mlibc-headers-only, gcc)	2m 3s
Build mlibc (x86_64, mlibc, clang)	51s
	1h 0m 7s

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