I’d re-arranged my project, which necessitated changing the include paths.
According to the ‘Console’ view, the build was successful - with zero warnings;
But, according to the ‘Problems’ view, there were 3 bad paths.
I eventually tracked this down to the fact that the include paths are duplicated under both ‘ARM ELF GCC C Compiler’ and ‘ARM ELF GCC C++ Compiler’ - I had only updated the ‘C’ ones, and not the C++ ones.
Because my project has no C++ files, the build was successful - but something was still complaining about the entries for the C++ compiler!
This is another annoyance with Eclipse - the way that there are so many different ways to affect one setting!
See also: viewtopic.php?f=108&t=4874