Makefile.in: Use LIBS from configure rather than specifying -lfcgi manually.

libfcgi needs libm and fcgiwrap does not use libtool or pkgconf to
detect libfcgi, so we need to add -lm explicitely when using static
libs.  Buildroot does this by providing LIBS=-lm to configure when
needed.  However fcgiwrap does not use Automake and its Makefile.in
ignores LIBS from configure.  Fix it with this patch.

Signed-off-by: Thomas Claveirole <thomas.claveirole@green-communications.fr>

diff -ur a/Makefile.in b/Makefile.in
--- a/Makefile.in	2013-02-03 14:25:17.000000000 +0100
+++ b/Makefile.in	2015-05-29 16:33:23.895280138 +0200
@@ -16,7 +16,7 @@
 	install -m 644 systemd/fcgiwrap.service $(DESTDIR)@systemdsystemunitdir@
 endif

-LDLIBS = -lfcgi @systemd_LIBS@
+LDLIBS = @LIBS@ @systemd_LIBS@
 CFLAGS = @AM_CFLAGS@

 fcgiwrap: fcgiwrap.c