[librsvg: 1/2] configure: Improve failures due to missing pkg-config

[Federico Mena Quintero <federico src gnome org>]

commit 0ce76d4df1846c66cb50fea1cd34e557cbf633f3
Author: Ismael Luceno <ismael iodev co uk>
Date:   Wed Dec 30 13:54:35 2020 +0100

    configure: Improve failures due to missing pkg-config
    
    Output a warning at the beginning, and fill PKG_CONFIG with "false" so
    that any auto-configuration attempts fail without bogus messages.

 configure.ac | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/configure.ac b/configure.ac
index ceb7cc12..3cec5c52 100644
--- a/configure.ac
+++ b/configure.ac
@@ -92,6 +92,9 @@ AM_PROG_CC_C_O
 AC_C_BIGENDIAN
 
 PKG_PROG_PKG_CONFIG
+AS_IF([test -z "$PKG_CONFIG"],
+  [AC_MSG_WARN([pkg-config is needed for auto-configuration of dependencies])
+   PKG_CONFIG=false])
 
 LT_INIT([win32-dll])
 LT_LIB_M