Fix linking on SmartOS/Illumos/Solaris. (#3)

In addition to the changes discussed in #2 manually specifying
libstackprotector (-lssp) as ld flag is needed to build bcrypt on
SmartOS.

rebar.config

@@ -7,7 +7,7 @@
 {port_env, [
   {"DRV_LDFLAGS","-shared $ERL_LDFLAGS -lpthread"},
   {"darwin", "DRV_LDFLAGS", "-bundle -flat_namespace -undefined suppress $ERL_LDFLAGS -lpthread"},
-  {"solaris", "ERL_LDFLAGS", "-lnsl $ERL_LDFLAGS"},
+  {"solaris", "ERL_LDFLAGS", "-lssp -lnsl $ERL_LDFLAGS"},
   {"DRV_CFLAGS","-Ic_src -Wall -fPIC $ERL_CFLAGS"},
   {"LDFLAGS", "$LDFLAGS -lpthread"}
 ]}.