configure: provide advice if PKG_PROG_PKG_CONFIG unavailable

These are the misleading error messages that this change prevents:
configure.ac:13: error: possibly undefined macro: AC_MSG_WARN
  If this token and others are legitimate, please use m4_pattern_allow.
  See the Autoconf documentation.
configure.ac:48: error: possibly undefined macro: AC_DEFINE
configure.ac:342: error: possibly undefined macro: AC_MSG_ERROR
configure.ac:608: error: possibly undefined macro: AC_MSG_NOTICE

Change-Id: I21bcc7715eeac0f3d0bcc60bba6801e6a895cdd0
Signed-off-by: R. Diez <rdiezmail-openocd@yahoo.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/7035
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

diff --git a/configure.ac b/configure.ac
index 7eada3a32e0aa19875a8fa716fb615c316a76d39..2d5cb5e29c208910ecb456215f4511b38e0c5d09 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -24,6 +24,12 @@ AC_PROG_CC
 m4_version_prereq([2.70],[],[AC_PROG_CC_C99])
 AM_PROG_CC_C_O
 AC_PROG_RANLIB
+
+# 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.]))])
 PKG_PROG_PKG_CONFIG([0.23])
 
 dnl disable checks for C++, Fortran and GNU Java Compiler