exim requires a C11 compiler so use ports-gcc.
With this it compiles on sparc64.

-- 
:wq Claudio

Index: Makefile
===================================================================
RCS file: /cvs/ports/mail/exim/Makefile,v
diff -u -p -r1.155 Makefile
--- Makefile	26 Nov 2025 09:19:30 -0000	1.155
+++ Makefile	15 Dec 2025 13:57:00 -0000
@@ -20,6 +20,10 @@ cWANTLIB =		c m
 WANTLIB-main =		${cWANTLIB} crypto execinfo iconv perl pcre2-8 ssl
 WANTLIB-eximon =	${cWANTLIB} X11 Xaw Xext Xmu Xt pcre2-8
 
+# needs C11 _Generic
+COMPILER =		base-clang ports-gcc
+COMPILER_LANGS =	c
+
 SITES =			https://ftp.exim.org/pub/exim/exim4/ \
 			https://ftp.exim.org/pub/exim/exim4/fixes/ \
 			https://ftp.exim.org/pub/exim/exim4/old/ \