bindings: cxx: link using the libtool archives

When linking with internal dependencies that were built with libtool the
most reliable method is to use the libtool archive (.la) files.

When building with slibtool it fails when it doesn't find the -lgpiod
linker flag, but if libgpiod is already installed to the system it will
be built using the system version instead of the newly built libraries.

Link: https://bugs.gentoo.org/913899
Signed-off-by: orbea <orbea@riseup.net>
[Bartosz: fix a typo in tests Makefile]
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

bindings/cxx/Makefile.am

@@ -24,8 +24,8 @@ libgpiodcxx_la_CXXFLAGS = -Wall -Wextra -g -std=gnu++17
 libgpiodcxx_la_CXXFLAGS += -fvisibility=hidden -I$(top_srcdir)/include/
 libgpiodcxx_la_CXXFLAGS += $(PROFILING_CFLAGS)
 libgpiodcxx_la_LDFLAGS = -version-info $(subst .,:,$(ABI_CXX_VERSION))
-libgpiodcxx_la_LDFLAGS += -lgpiod -L$(top_builddir)/lib
 libgpiodcxx_la_LDFLAGS += $(PROFILING_LDFLAGS)
+libgpiodcxx_la_LIBADD = $(top_builddir)/lib/libgpiod.la
 
 include_HEADERS = gpiod.hpp
 

bindings/cxx/examples/Makefile.am

@@ -3,7 +3,7 @@
 
 AM_CXXFLAGS = -I$(top_srcdir)/bindings/cxx/ -I$(top_srcdir)/include
 AM_CXXFLAGS += -Wall -Wextra -g -std=gnu++17
-AM_LDFLAGS = -lgpiodcxx -L$(top_builddir)/bindings/cxx/
+LDADD = $(top_builddir)/bindings/cxx/libgpiodcxx.la
 
 noinst_PROGRAMS = \
 	async_watch_line_value \

bindings/cxx/tests/Makefile.am

@@ -4,9 +4,9 @@
 AM_CXXFLAGS = -I$(top_srcdir)/bindings/cxx/ -I$(top_srcdir)/include
 AM_CXXFLAGS += -I$(top_srcdir)/tests/gpiosim/
 AM_CXXFLAGS += -Wall -Wextra -g -std=gnu++17 $(CATCH2_CFLAGS)
-AM_LDFLAGS = -lgpiodcxx -L$(top_builddir)/bindings/cxx/
-AM_LDFLAGS += -lgpiosim -L$(top_builddir)/tests/gpiosim/
-AM_LDFLAGS += -pthread
+AM_LDFLAGS = -pthread
+LDADD = $(top_builddir)/bindings/cxx/libgpiodcxx.la
+LDADD += $(top_builddir)/tests/gpiosim/libgpiosim.la
 
 noinst_PROGRAMS = gpiod-cxx-test