Hi list,
So I think I figured out the answer myself.
The essence here is that Clang 2.6, 2.7 and 2.8 wouldn't even compile Gambit, and 2.9-3.1 would compile Gambit but be fairly slow.
A lot has happened since Clang 3.1, which is the last Clang version covered by install.txt today. The latest version today is 6.0. Ref.
https://en.wikipedia.org/wiki/Clang#Status_history . Clang is now the default C/C++/Objective-C compiler choice in a handful operating systems, for AMD64 and some more architectures.
The term "LLVM" only denotes that Clang has an internal intermediary language form, and the term LLVM has no other meaning in the direction of executable bytecode like Java JIT VM:s. I.e. Clang is only a native C/C++/Obj-C compiler. A list of the Clang/LLVM projects is on the main page at
http://www.llvm.org/ .
I have not tested yet but I do expect Clang to run Gambit stably and at a totally-okay speed.
Adam