mm: Add mpagemap #891

Job	Run time
build-minimal-sysroots (x86_64)	48s
build-minimal-sysroots (riscv64)	58s
build-minimal-sysroots (arm64)	50s
build-toolchains (ubuntu-latest, x86_64, gnu)	51s
build-toolchains (ubuntu-latest, riscv64, gnu)	40s
build-toolchains (ubuntu-latest, arm64, gnu)	42s
build-toolchains (ubuntu-20.04, x86_64, gnu)	37s
build-toolchains (ubuntu-20.04, riscv64, gnu)	35s
build-toolchains (ubuntu-20.04, arm64, gnu)	25s
build-toolchains (macos-latest, x86_64, gnu)	1m 24s
build-toolchains (macos-latest, riscv64, gnu)	1m 14s
build-toolchains (macos-latest, arm64, gnu)	58s
build-toolchains (ubuntu-latest, llvm, all)	1m 30s
build-riscv	2m 30s
build-llvm-riscv64	2m 27s
build	2m 58s
build-arm64	2m 41s
build-llvm	3m 0s
build-llvm-arm64	2m 39s
run-x86_64	0s
run-riscv64-llvm	0s
run-riscv	0s
run-x86_64-llvm	0s
	27m 47s

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