Use it to enhance the BASEDIR / OPAMTMP detection #414

Job	Run time
Analyse	10s
Cygwin	5s
Build-macOS (4.14.1)	5m 24s
Build-Linux (4.08.1)	42s
Hygiene	31s
Build-Linux (4.09.1)	25s
Test-macOS (4.14.1)	58m 19s
Build-Linux (4.10.2)	37s
Build-Linux (4.11.2)	41s
Build-Linux (4.12.1)	42s
Build-Linux (4.13.1)	42s
Build-Linux (5.0.0)	41s
Build-Linux (5.1.0)	30s
Build-Linux (4.14.1)	41s
Build-Windows (x86_64-pc-cygwin, x86_64-pc-cygwin, 4.14.1)	41m 11s
Build-Windows (i686-w64-mingw32, x86_64-pc-cygwin, 4.14.1)	1h 15m 27s
Build-Windows (x86_64-w64-mingw32, x86_64-pc-cygwin, 4.14.1)	1h 15m 30s
Build-Windows (i686-pc-windows, x86_64-pc-cygwin, 4.14.1)	1h 15m 30s
Build-Windows (x86_64-pc-windows, x86_64-pc-cygwin, 4.14.1)	51m 0s
Cold-Linux	0s
Upgrade-Linux	0s
Solvers-Linux	0s
Test-Linux	0s
Upgrade-macOS (4.14.1)	2m 41s
Solvers-macOS (z3, 4.14.1)	1m 58s
Solvers-macOS (0install, 4.14.1)	2m 24s
	6h 35m 51s

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