build: Improve error message when pkg-config is not installed

Author: hebasto

configure.ac

@@ -13,7 +13,7 @@ AC_CONFIG_HEADERS([src/config/bitcoin-config.h])
 AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_MACRO_DIR([build-aux/m4])
 
-m4_ifndef([PKG_PROG_PKG_CONFIG], [AC_MSG_ERROR([PKG_PROG_PKG_CONFIG macro not found. Please install pkg-config and re-run autogen.sh])])
+m4_ifndef([PKG_PROG_PKG_CONFIG], [m4_fatal([PKG_PROG_PKG_CONFIG macro not found. Please install pkg-config and re-run autogen.sh])])
 PKG_PROG_PKG_CONFIG
 if test "$PKG_CONFIG" = ""; then
   AC_MSG_ERROR([pkg-config not found])