Fix build-system: use xxx_LDADD instead of xxx_LDFLAGS

xxx_LDFLAGS place the libraries like '-lX11' or '-lXft' at the beginning of
the linker command. Some systems were not able to handle the situation and
this lead to a lot of unresolved symbols. Reading the documentation of
automake:

    ... you can use LDADD to do so. This variable is used to specify
    additional objects or libraries to link with; it is inappropriate for
    specifying specific linker flags, you should use AM_LDFLAGS for this
    purpose.

In addition we link against -lm in order to satisfy symbols refering to 'cos'
and 'sin'.

1 files changed, 4 insertions, 0 deletions

diff --git a/configure.ac b/configure.ac
index 65ee23e..33217ad 100644
--- a/configure.ac
+++ b/configure.ac
@@ -129,6 +129,10 @@ AC_CHECK_FUNCS([ \
         vsnprintf \
 ])
 
+AC_CHECK_LIBM
+AC_SUBST(LIBM)
+LIBS="$LIBS $LIBM"
+
 dnl Windows requires the mingw-catgets library for the catgets function.
 AC_SEARCH_LIBS([catgets], [catgets], [], [])