The base c++ compiler is not good enough to compile hdf5.
Since this is already depending on ports-gcc just use it also for c++.

Code fails because of missing cinttypes include.

With this I can build hdf5 on sparc64 (using gcc15 but gcc8 may work as
well)
-- 
:wq Claudio

Index: Makefile
===================================================================
RCS file: /cvs/ports/math/hdf5/Makefile,v
diff -u -p -r1.30 Makefile
--- Makefile	5 Sep 2025 22:33:59 -0000	1.30
+++ Makefile	5 Nov 2025 10:58:46 -0000
@@ -29,7 +29,7 @@ PERMIT_PACKAGE =	Yes
 WANTLIB += c m ${COMPILER_LIBCXX} z aec sz
 
 COMPILER =		base-clang ports-gcc base-gcc
-COMPILER_LANGS =	fortran
+COMPILER_LANGS =	c++ fortran
 
 # for h5fuse.sh
 RUN_DEPENDS +=		shells/bash