Do not look for json-c.
https://gitlab.freedesktop.org/fontconfig/fontconfig/issues/108
--- configure.orig	2023-01-27 02:22:13.000000000 -0600
+++ configure	2023-01-28 19:44:08.000000000 -0600
@@ -19226,7 +19226,7 @@
 
 if test -n "$JSONC_CFLAGS"; then
     pkg_cv_JSONC_CFLAGS="$JSONC_CFLAGS"
- elif test -n "$PKG_CONFIG"; then
+ elif test -n ""; then
     if test -n "$PKG_CONFIG" && \
     { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"json-c\""; } >&5
   ($PKG_CONFIG --exists --print-errors "json-c") 2>&5
@@ -19243,7 +19243,7 @@
 fi
 if test -n "$JSONC_LIBS"; then
     pkg_cv_JSONC_LIBS="$JSONC_LIBS"
- elif test -n "$PKG_CONFIG"; then
+ elif test -n ""; then
     if test -n "$PKG_CONFIG" && \
     { { printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$PKG_CONFIG --exists --print-errors \"json-c\""; } >&5
   ($PKG_CONFIG --exists --print-errors "json-c") 2>&5