Use monotonic clock for sequence numbering #135

Job	Run time
build (clang)	8m 26s
build (clang, CFLAGS=-flto LDFLAGS=-flto)	8m 27s
build (gcc)	9m 3s
build (gcc, CFLAGS=-flto LDFLAGS=-flto)	8m 27s
build (gcc-9, NO_32BIT_TEST=1 AR=gcc-ar-9 NM=gcc-nm-9 RANLIB=gcc-ranlib-9 )	6m 14s
build (gcc-10, NO_32BIT_TEST=1 AR=gcc-ar-10 NM=gcc-nm-10 RANLIB=gcc-ranlib-10 )	6m 5s
build (gcc-10, NO_32BIT_TEST=1 AR=gcc-ar-10 NM=gcc-nm-10 RANLIB=gcc-ranlib-10 CFLAGS=-flto LDFLAG...	5m 56s
build (gcc-12, NO_32BIT_TEST=1 AR=gcc-ar-12 NM=gcc-nm-12 RANLIB=gcc-ranlib-12 )	5m 57s
build (gcc-12, NO_32BIT_TEST=1 AR=gcc-ar-12 NM=gcc-nm-12 RANLIB=gcc-ranlib-12 CFLAGS=-flto LDFLAG...	5m 50s
	1h 4m 25s

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