Fix linking with internal libraries.

When building fflas-ffpack with slibtool it fails.

ld: cannot find -lfflas
ld: cannot find -lffpack

This reveals several issues.

* Internal libraries should never link with linker flags and
  should use the libtool archive (.la) files instead.
* These should be added to LIBADD for libraries or LDADD for
  programs and never to LDFLAGS which is only for other linker
  flags.
* The _DEPENDENCIES do not need to be set manually since they
  the defaults will be correct if the LIBADD/LDADD variables
  are set correctly.
* This issue is masked if fflas-ffpack is already installed
  where -lfflas and -lffpack are found installed on the system
  and not in the build directory.

Making these changes allows both slibtool and GNU libtool to
build correctly, the latter is far more permissive and silently
hides this issue.

fflas-ffpack/interfaces/libs/Makefile.am

@@ -60,27 +60,24 @@ libfflas_la_LDFLAGS=  $(LDADD) -version-info 1:0:0 \
 
 libffpack_la_SOURCES= ffpack_inst.C \
 		      ffpack_inst_implem.inl
+libffpack_la_LIBADD= libfflas.la
 libffpack_la_LDFLAGS= $(LDADD) -version-info 1:0:0 \
-		       -no-undefined $(top_builddir)/fflas-ffpack/interfaces/libs/libfflas.la
-
-EXTRA_libffpack_la_DEPENDENCIES= libfflas.la
+		       -no-undefined
 
 libfflas_c_la_SOURCES=fflas_lvl1.C \
 		    fflas_lvl2.C \
 		    fflas_lvl3.C \
 		    fflas_sparse.C
 #libfflas_c_la_CPPFLAGS=$(AM_CPPFLAGS) -DFFLAS_COMPILED -DFFPACK_COMPILED
+libfflas_c_la_LIBADD= libfflas.la
 libfflas_c_la_LDFLAGS=  $(LDADD) -version-info 1:0:0 \
-                       -no-undefined 	$(top_builddir)/fflas-ffpack/interfaces/libs/libfflas.la
-
-EXTRA_libfflas_c_la_DEPENDENCIES=libfflas.la
+                       -no-undefined
 
 libffpack_c_la_SOURCES=ffpack.C
 #libffpack_c_la_CPPFLAGS=$(AM_CPPFLAGS) -DFFLAS_COMPILED -DFFPACK_COMPILED
+libffpack_c_la_LIBADD= libfflas.la libffpack.la
 libffpack_c_la_LDFLAGS=  $(LDADD) -version-info 1:0:0 \
-		        -no-undefined -lfflas -lffpack
-EXTRA_libffpack_c_la_DEPENDENCIES=libffpack.la
-
+		        -no-undefined
 
 EXTRA_DIST=c_libs.doxy