Use stol() for determining Linux memory use #65

Job	Run time
build linux-arm64 Release	59s
build linux-arm64 Debug	59s
build linux-arm64-musl Release	49s
build linux-arm64-musl Debug	51s
build linux-armv5 Release	58s
build linux-armv5 Debug	56s
build linux-armv5-musl Release	56s
build linux-armv5-musl Debug	59s
build linux-armv6 Release	57s
build linux-armv6 Debug	57s
build linux-armv6-musl Release	51s
build linux-armv6-musl Debug	50s
build linux-armv7 Release	59s
build linux-armv7 Debug	57s
build linux-armv7a Release	57s
build linux-armv7a Debug	58s
build linux-armv7l-musl Release	48s
build linux-armv7l-musl Debug	49s
build linux-x64-clang Release	1m 1s
build linux-x64-clang Debug	1m 2s
build linux-s390x Release	1m 0s
build linux-s390x Debug	58s
build linux-x64 Release	41s
build linux-x64 Debug	43s
build linux-x86 Release	46s
build linux-x86 Debug	45s
build linux-mips Release	57s
build linux-mips Debug	59s
build linux-ppc64le Release	54s
build linux-ppc64le Debug	52s
build manylinux1-x64 Release	52s
build manylinux1-x64 Debug	48s
build manylinux1-x86 Release	45s
build manylinux1-x86 Debug	46s
build manylinux2010-x64 Release	38s
build manylinux2010-x64 Debug	39s
build manylinux2010-x86 Release	40s
build manylinux2010-x86 Debug	41s
build manylinux2014-x64 Release	1m 18s
build manylinux2014-x64 Debug	1m 16s
build manylinux2014-x86 Release	1m 15s
build manylinux2014-x86 Debug	1m 15s
build linux-riscv64 Release	57s
build linux-riscv64 Debug	58s
build linux-riscv32 Release	51s
build linux-riscv32 Debug	52s
	41m 39s

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