build: fail with a useful error message if pkg-config isn't available

diff --git a/m4/libevent_openssl.m4 b/m4/libevent_openssl.m4
index 178cf3872b2f949cae1b5f3cecfcc4c5e04a312b..1adc583f44b7e3e799db7032a2f1c6ad91959b01 100644 (file)
--- a/m4/libevent_openssl.m4
+++ b/m4/libevent_openssl.m4
@@ -1,6 +1,9 @@
 dnl ######################################################################
 dnl OpenSSL support
 AC_DEFUN([LIBEVENT_OPENSSL], [
+
+m4_ifndef([PKG_PROG_PKG_CONFIG], [AC_MSG_ERROR([PKG_PROG_PKG_CONFIG not found. Please install pkg-config and re-run autogen.sh])])
+
 PKG_PROG_PKG_CONFIG([0.15.0])
 
 case "$host_os" in