See https://trac.macports.org/ticket/62428 for the same issue.

--- configure.ac.orig	2020-10-09 06:51:29.000000000 -0700
+++ configure.ac	2021-03-26 21:00:44.000000000 -0700
@@ -9,6 +9,7 @@
 AC_CANONICAL_HOST
 
 AC_PROG_CC
+AC_PROG_CPP
 AM_PROG_CC_C_O
 AC_PROG_LIBTOOL
 PKG_PROG_PKG_CONFIG