Unhack the string_view workaround in llpreviewgesture, with a slightly less hacky hack in llstring. lol. Thanks Liru for making this as lean as ancient gcc can stand it to be.

indra/llcommon/llstring.h

@@ -29,6 +29,16 @@
 
 #include <boost/optional/optional.hpp>
 #include <string>
+
+#if __cplusplus < 201606
+#include <absl/strings/string_view.h>
+namespace std {
+    typedef absl::string_view string_view;
+}
+#else
+    #include <string_view>
+#endif
+
 #include <cstdio>
 //#include <locale>
 #include <iomanip>