[coreboot] inteltool and sys/io.h

[Trammell Hudson]

When cross compiling inteltool with musl-libc the <sys/io.h> header
is not included due to this test in inteltool.h:

#if defined(__GLIBC__)
#include <sys/io.h>
#endif

Unfortunately I'm not sure what the right test is here, since
the musl libc team is opposed to having a __MUSL__ define:

http://openwall.com/lists/musl/2013/03/29/13