sysdeps/managarm: Implement sysconf request #995

Job	Run time
Compile sysdeps (dripos)	2m 4s
Compile sysdeps (lemon)	2m 6s
Build mlibc (x86_64, mlibc, gcc)	3m 32s
Build mlibc (x86_64, mlibc-static, gcc)	3m 26s
Compile sysdeps (aero)	2m 5s
Compile sysdeps (ironclad)	2m 5s
Build mlibc (x86_64, mlibc-shared, gcc)	3m 1s
Compile sysdeps (lyre)	2m 5s
Build mlibc (x86_64, mlibc-ansi-only, gcc)	2m 52s
Compile sysdeps (keyronex)	2m 6s
Build mlibc (x86_64, mlibc-headers-only, gcc)	1m 53s
Compile sysdeps (managarm)	1m 59s
Build mlibc (riscv64, mlibc, gcc)	3m 39s
Compile sysdeps (vinix)	2m 4s
Build mlibc (riscv64, mlibc-static, gcc)	4m 37s
Build mlibc (riscv64, mlibc-shared, gcc)	2m 59s
Build mlibc (riscv64, mlibc-ansi-only, gcc)	2m 49s
Build mlibc (riscv64, mlibc-headers-only, gcc)	1m 51s
Build mlibc (aarch64, mlibc, gcc)	3m 54s
Build mlibc (aarch64, mlibc-static, gcc)	3m 26s
Build mlibc (aarch64, mlibc-shared, gcc)	3m 13s
Build mlibc (aarch64, mlibc-ansi-only, gcc)	3m 14s
Build mlibc (aarch64, mlibc-headers-only, gcc)	1m 52s
Build mlibc (x86, mlibc, gcc)	3m 47s
Build mlibc (x86, mlibc-static, gcc)	3m 26s
Build mlibc (x86, mlibc-shared, gcc)	3m 15s
Build mlibc (x86, mlibc-ansi-only, gcc)	3m 13s
Build mlibc (x86, mlibc-headers-only, gcc)	1m 50s
Build mlibc (x86_64, mlibc, clang)	3m 30s
	1h 21m 53s

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