Build on MIPS (GNU/Linux): LDFLAGS needs libdl

Hello,

I am on a mips64el-unknown-linux-gnu platform. I have built netsurf
and had to replace the following line in gtk/Makefile.target:

LDFLAGS += -lm

by this one:

LDFLAGS += -lm -ldl

Can this change be applied in netsurf branch?

Christophe