remove gcc_unused

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/lib/sqlite/Util.hxx

@@ -54,7 +54,7 @@ Bind(sqlite3_stmt *stmt, unsigned i, const char *value)
 
 template<typename... Args>
 static void
-BindAll2(gcc_unused sqlite3_stmt *stmt, gcc_unused unsigned i)
+BindAll2([[maybe_unused]] sqlite3_stmt *stmt, [[maybe_unused]] unsigned i)
 {
 	assert(int(i - 1) == sqlite3_bind_parameter_count(stmt));
 }