Autoconf 2.72 seems to be under preparation upstream, I therefore started to build dependent components to verify that they can be built once it lands in Fedora.

Your component fails to build with the new version of autoconf, due to the following error:

---
checking FONTCONFIG_CFLAGS... -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/harfbuzz -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/sysprof-4 -pthread -I/usr/include/libxml2 
checking FONTCONFIG_LIBS... -lfontconfig -lfreetype 
./configure: line 22265: syntax error near unexpected token `;;'
./configure: line 22265: `		 ;;'
error: Bad exit status from /var/tmp/rpm-tmp.ENLWto (%build)
    Bad exit status from /var/tmp/rpm-tmp.ENLWto (%build)
RPM build errors:
Child return code was: 1
---

The error is due to under-quoting of AS_IF parameters in configure.ac.

The proposed patch is the following:

---
diff -U5 -r synfig-1.5.1.old/configure.ac synfig-1.5.1/configure.ac
--- synfig-1.5.1.old/configure.ac	2022-11-24 10:38:52.696511899 +0100
+++ synfig-1.5.1/configure.ac	2022-11-24 10:39:14.000290334 +0100
@@ -256,12 +256,12 @@
 )
 
 AS_IF([test "x$with_harfbuzz" != xno],
 	[
 		AS_IF([test "x$with_freetype" != xyes],
-			AC_MSG_FAILURE(
-				[--with-harfbuzz was given, but it depends on --with-freetype])
+			[AC_MSG_FAILURE(
+				[--with-harfbuzz was given, but it depends on --with-freetype])]
 		)
 	]
 )
 
 AS_IF([test "x$with_harfbuzz" != xno],
---

Please have a look and get the problem fixed upstream.