[gcalctool] Add missing -lm linker flag

[Robert Ancell <rancell src gnome org>]

commit d0004fd5d9432765570186b7dcb4a2e8c580df68
Author: Stefano Facchini <stefano facchini gmail com>
Date:   Sun Oct 14 11:46:09 2012 +0200

    Add missing -lm linker flag
    
    https://bugzilla.gnome.org/show_bug.cgi?id=686106

 src/Makefile.am |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index 3d0e827..d5da77b 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -38,7 +38,8 @@ gcalctool_VALAFLAGS = \
 	--pkg libxml-2.0
 
 gcalctool_LDADD = \
-	$(GCALCTOOL_LIBS)        
+	$(GCALCTOOL_LIBS) \
+	-lm
 
 gcalccmd_SOURCES = \
 	config.vapi \