+
+# If macro PKG_PROG_PKG_CONFIG is not available, Autoconf generates a misleading error message,
+# so check for existence first, and otherwise provide helpful advice.
+m4_ifndef([PKG_PROG_PKG_CONFIG], [m4_fatal(m4_normalize([
+ Macro PKG_PROG_PKG_CONFIG is not available.
+ It is usually defined in file pkg.m4 provided by package pkg-config.]))])