On glibc systems, argp is provided by libc.  However, on
uclibc and other systems which lack argp in their C library,
argp might be provided by a stand alone library, libargp.
This patch adds tests to the build system to find who provides
argp.

X-Gentoo-Bug: 292191
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=292191
Reported-by: Ed Wildgoose <gentoo@wildgooses.com>
Signed-off-by: Anthony G. Basile <blueness@gentoo.org>


--- a/configure.ac
+++ b/configure.ac
@@ -47,6 +47,28 @@
 dnl Checks for optional library functions
 dnl -------------------------------------
 
+dnl First check if we have argp available from libc
+AC_LINK_IFELSE(
+	[AC_LANG_PROGRAM(
+		[#include <argp.h>],
+		[int argc=1; char *argv[]={"test"}; argp_parse(0,argc,argv,0,0,0); return 0;]
+		)],
+	[libc_has_argp="true"],
+	[libc_has_argp="false"]
+)
+
+dnl If libc doesn't provide argp, then test for libargp
+if test "$libc_has_argp" = "false" ; then
+	AC_MSG_WARN("libc does not have argp")
+	AC_CHECK_LIB([argp], [argp_parse], [have_argp="true"], [have_argp="false"])
+
+	if test "$have_argp" = "false"; then
+		AC_MSG_ERROR("no libargp found")
+	else
+		LIBS+=" -largp"
+	fi
+fi
+
 dnl -----------------
 dnl Configure options
 dnl -----------------