macos-xcode-cmake build fails with --std=c++17 SOLVED

[pdv]

I suppose HAVE_DEF_MAKE_UNIQUE should have been set to one but it wasn't.
Removing HAVE_DEF_MAKE_UNIQUE from cmake's cache didn't help.
The check_cxx_source_compiles() in ConfigureChecks.cmake was never 
executed and HAVE_DEF_MAKE_UNIQUE was never set.

In the end I started from scratch and then the check ran and 
HAVE_DEF_MAKE_UNIQUE=1.

P. De Visschere