https://bugs.gentoo.org/904515
https://github.com/HDFGroup/hdf5/issues/2422
https://github.com/HDFGroup/hdf5/issues/2621
https://github.com/HDFGroup/hdf5/pull/2667
https://github.com/HDFGroup/hdf5/commit/b77cb393b884c1dbdaffb300aa8c4967d9ba7fb0

From b77cb393b884c1dbdaffb300aa8c4967d9ba7fb0 Mon Sep 17 00:00:00 2001
From: jhendersonHDF <jhenderson@hdfgroup.org>
Date: Tue, 11 Apr 2023 14:31:25 -0500
Subject: [PATCH] Fix improper include of build directory (#2422, #2621)
 (#2667)

--- a/configure.ac
+++ b/configure.ac
@@ -3012,8 +3012,7 @@ SUBFILING_VFD=no
 HAVE_MERCURY="no"
 
 ## Always include subfiling directory so public header files are available
-CPPFLAGS="$CPPFLAGS -I$ac_abs_confdir/src/H5FDsubfiling"
-AM_CPPFLAGS="$AM_CPPFLAGS -I$ac_abs_confdir/src/H5FDsubfiling"
+H5_CPPFLAGS="$H5_CPPFLAGS -I$ac_abs_confdir/src/H5FDsubfiling"
 
 AC_MSG_CHECKING([if the subfiling I/O virtual file driver (VFD) is enabled])
 
@@ -3061,8 +3060,7 @@ if test "X$SUBFILING_VFD" = "Xyes"; then
     mercury_dir="$ac_abs_confdir/src/H5FDsubfiling/mercury"
     mercury_inc="$mercury_dir/src/util"
 
-    CPPFLAGS="$CPPFLAGS -I$mercury_inc"
-    AM_CPPFLAGS="$AM_CPPFLAGS -I$mercury_inc"
+    H5_CPPFLAGS="$H5_CPPFLAGS -I$mercury_inc"
 
     HAVE_STDATOMIC_H="yes"
     AC_CHECK_HEADERS([stdatomic.h],,[HAVE_STDATOMIC_H="no"])