Speedup OpamSystem.read by 8% #2772

Job	Run time	Billable time
Analyse	7s	0s
Cygwin	6s	0s
Hygiene	25s	0s
Build-Linux (4.08.1)	2m 1s	0s
Build-macOS (4.14.1)	2m 21s	0s
Build-Linux (4.09.1)	1m 51s	0s
Build-Linux (4.10.2)	3m 6s	0s
Test-macOS (4.14.1)	27m 48s	0s
Build-Linux (4.11.2)	1m 49s	0s
Build-Linux (4.12.1)	2m 13s	0s
Build-Linux (4.13.1)	1m 58s	0s
Build-Linux (5.0.0)	2m 35s	0s
Build-Linux (5.1.1)	1m 45s	0s
Build-Linux (4.14.1)	2m 4s	0s
Build-Windows (x86_64-pc-cygwin, x86_64-pc-cygwin, 4.14.1)	38m 31s	0s
Build-Windows (i686-w64-mingw32, x86_64-pc-cygwin, 4.14.1)	46m 59s	0s
Build-Windows (x86_64-w64-mingw32, x86_64-pc-cygwin, 4.14.1)	46m 27s	0s
Build-Windows (i686-pc-windows, x86_64-pc-cygwin, 4.14.1)	52m 29s	0s
Build-Windows (x86_64-pc-windows, x86_64-pc-cygwin, 4.14.1)	49m 20s	0s
Solvers-macOS (z3, 4.14.1)	1m 24s	0s
Solvers-macOS (0install, 4.14.1)	1m 52s	0s
Upgrade-macOS (4.14.1)	1m 32s	0s
Test-Linux (4.14.1)	14m 48s	0s
Cold-Linux	5m 20s	0s
Solvers-Linux (z3, 4.14.1)	52s	0s
Upgrade-Linux (4.14.1)	1m 28s	0s
Solvers-Linux (0install, 4.14.1)	1m 44s	0s
	5h 12m 55s	0s

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