configure.ac: warn when pkg-config is not installed

It hasn't been optional for a while now.

Fixes:
checking for rrd.h... no
./configure: 25157: Syntax error: word unexpected (expecting ")")

Signed-off-by: Florian Forster <octo@collectd.org>

diff --git a/configure.ac b/configure.ac
index 6cdfcd6..f623263 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -54,6 +54,10 @@ AC_DISABLE_STATIC
 AC_PROG_LIBTOOL
 AC_PROG_LEX
 AC_PROG_YACC
+
+# Warn when pkg.m4 is missing
+m4_pattern_forbid([^_?PKG_[A-Z_]+$],[*** pkg.m4 missing, please install pkg-config])
+
 PKG_PROG_PKG_CONFIG
 
 AC_CHECK_PROG([have_protoc_c], [protoc-c], [yes], [no])