[devhelp] build: Make sure to link LIBM

[Rico Tzschichholz <ricotz src gnome org>]

commit a9609eb8ab2a5a158d6de09ebb4facde1618a3e7
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Thu May 4 09:09:34 2017 +0200

    build: Make sure to link LIBM
    
    Follows the changes of 20abd844bbebbb5a662036fd4c4c832794e4a8a0

 src/Makefile.am |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index 217b0d5..84941db 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -151,6 +151,7 @@ devhelp_CFLAGS =            \
 
 devhelp_LDADD =                \
        $(DEVHELP_LIBS)         \
+       $(LIBM)                 \
         libdevhelp-3.la
 
 devhelp_LDFLAGS =      \