Since clang defines __GNUC__ and __regparm__ is not valid on arm the wrong defines are used in attributes.h. As far as I understood __regparm__ is only valid on x86, so make sure this is only used on x86. The same error shows up on aarch64, it should be fixed there too. I can't test it there.
I can't add the patches directory with a read only CVS server, so here is the patch inline: $OpenBSD$ Index: src/attributes.h --- src/attributes.h.orig +++ src/attributes.h @@ -67,7 +67,7 @@ #define attribute_inline __inline__ -#if GNUC_MINIMUM(2,7) /* doesn't work reliable before, IIRC */ +#if GNUC_MINIMUM(2,7) && (defined(__amd64__) || defined(__i386__)) # define attribute_regparm(x) __attribute__((__regparm__((x)))) #else # define attribute_regparm(x)
