[folks] build: Add dependency on libm for the BlueZ backend

[Philip Withnall <pwithnall src gnome org>]

commit bc9e0684504c32b71ee2913d48ee8298e8468d46
Author: Philip Withnall <philip withnall collabora co uk>
Date:   Tue Jan 20 10:26:50 2015 +0000

    build: Add dependency on libm for the BlueZ backend
    
    It uses Math.pow().

 backends/bluez/Makefile.am |    1 +
 configure.ac               |    2 ++
 2 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/backends/bluez/Makefile.am b/backends/bluez/Makefile.am
index f644687..5ab9d6e 100644
--- a/backends/bluez/Makefile.am
+++ b/backends/bluez/Makefile.am
@@ -32,6 +32,7 @@ bluez_la_CFLAGS = \
 bluez_la_LIBADD = \
        $(backend_libadd) \
        $(EBOOK_LIBS) \
+       $(LIBM) \
        $(NULL)
 
 bluez_la_LDFLAGS = \
diff --git a/configure.ac b/configure.ac
index 06167b1..1b906f1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -360,6 +360,8 @@ AS_IF([test x$enable_bluez_backend = xyes], [
 
         AM_PROG_VALAC([0.22.0.45-383d-dirty],
                       [have_valac_0_22_2=yes], [have_valac_0_22_2=no])
+
+        LT_LIB_M
 ])
 
 # The BlueZ tests are conditional on several bleeding-edge dependencies.