[PATCH][libgpiod] Make bitset_cmp::operator() const.

[Michael Beach <michaelb@xxxxxxxx>]

This fixes build problems with clang and libc++, and such constness is
now required by C++17 (see https://cplusplus.github.io/LWG/issue2542).

Signed-off-by: Michael Beach <michaelb@xxxxxxxx>
---
 bindings/cxx/line_bulk.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/bindings/cxx/line_bulk.cpp b/bindings/cxx/line_bulk.cpp
index c93f364..e52d33d 100644
--- a/bindings/cxx/line_bulk.cpp
+++ b/bindings/cxx/line_bulk.cpp
@@ -29,7 +29,7 @@ const ::std::map<int, int> reqtype_mapping = {
 
 struct bitset_cmp
 {
-	bool operator()(const ::std::bitset<32>& lhs, const ::std::bitset<32>& rhs)
+	bool operator()(const ::std::bitset<32>& lhs, const ::std::bitset<32>& rhs) const
 	{
 		return lhs.to_ulong() < rhs.to_ulong();
 	}
-- 
2.17.1