[gnome-sudoku/vala-port] Build fix

[Thomas Hindoe Paaboel Andersen <thomashpa src gnome org>]

commit 7bc9c15189ef76c038dbd9827a000233a8f2a6a9
Author: Thomas Hindoe Paaboel Andersen <phomes gmail com>
Date:   Sun Jun 9 23:30:22 2013 +0200

    Build fix

 src/Makefile.am |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index ffcd557..114cba9 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -23,7 +23,8 @@ gnome_sudoku_CFLAGS = \
        $(GNOME_SUDOKU_CFLAGS)
 
 gnome_sudoku_LDADD = \
-       $(GNOME_SUDOKU_LIBS)
+       $(GNOME_SUDOKU_LIBS) \
+       -lm
 
 gnome_sudoku_VALAFLAGS = \
        --pkg posix \