dvblast: fix static linking

dvblast links to -lev, wihch uses functions from the maths library,
like floor().

When linking to a shared libev.so, that dependency is automatically
pulled in because libev as a DT_NEEDED ELF tag on libm.so.

But when lnking to the static libev.a, since there is no way to express
such dependencies in static libraries, libm is not pulled in, which
leads to build failures such as;
    http://autobuild.buildroot.org/results/1f0/1f02f84fb926839a1adbe3af457bb909fdc44433/build-end.log

Fix that by always linking to -lm (which must come *after* -lev).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>

diff -durN dvblast-3.0.orig/Makefile dvblast-3.0/Makefile
--- dvblast-3.0.orig/Makefile	2015-10-05 17:51:14.000000000 +0200
+++ dvblast-3.0/Makefile	2015-10-30 15:57:19.547123894 +0100
@@ -28,7 +28,7 @@
 LDLIBS += -lstreammaster
 endif
 
-LDLIBS_DVBLAST += -lpthread -lev
+LDLIBS_DVBLAST += -lpthread -lev -lm
 
 OBJ_DVBLAST = dvblast.o util.o dvb.o udp.o asi.o demux.o output.o en50221.o comm.o mrtg-cnt.o asi-deltacast.o
 OBJ_DVBLASTCTL = util.o dvblastctl.o