How to suppress header file warnings from an Xcode project

When I build UnzipKit in Xcode 7 beta 4, I'm getting a compiler warning in MiniZip's ioapi.h file. For example:

.../ioapi.h:22:9: warning: macro name is a reserved identifier [-Wreserved-id-macro]
#define _ZLIBIOAPI64_H

ioapi.c has many of its own warnings, so I compile it with -Wno-everything like so:

However, there is no "Compiler Flags" setting available for the headers:

How can I silence the warning without modifying the source file? I'd rather not modify it, as it's an external dependency. I also don't want to turn it on for the whole project, because it's a useful warning for my own code.