The viewer compiles fine on my Catalina Hackintosh VirtualBox VM, using Xcode 12. Not owning a Mac, and newer macOS versions not properly installing as VMs, I
cannot guarantee that newer Xcode versions (themselves requiring newer macOS versions) are able to build the viewer...
This issue seems however to be specific to Xcode 16.3 itself, which removed support for
std::char_traits<unsigned short>. See the Deprecations chapter in
Xcode 16.3 release notes.
I came up with this patch, that might work (let me know)... It still compiles with Xcode 12, at least:
Apply from a terminal pointing inside the linden/ sources directory, with:
patch -p1 -s </path_to_patch/Xcode16.3-char16_t-patch.txtAlternatively, compiling with Xcode 16.2 should make it.