check for presense of the patch utility

Author: dimpase

configure.ac

@@ -220,6 +220,14 @@ then
     AC_MSG_ERROR([Exiting, as the archiver 'ar' can not be found.])
 fi
 
+AC_CHECK_PROG(found_patch, patch, yes, no)
+if test x$found_patch != xyes
+then
+    AC_MSG_NOTICE([Sorry, the 'patch' command must be in the path to build AC_PACKAGE_NAME])
+    AC_MSG_NOTICE([See e.g. https://www.gnu.org/software/patch/])
+    AC_MSG_ERROR([Exiting, as the utility 'patch' can not be found.])
+fi
+
 AC_CHECK_PROG(found_m4, m4, yes, no)
 if test x$found_m4 != xyes
 then