atomic: check if -latomic is required for std::atomic

* configure.ac,
m4/l_atomic.m4,
python/Makefile.am,
tests/Makefile.am: Here.

python/Makefile.am

@@ -23,7 +23,7 @@
 AUTOMAKE_OPTIONS = subdir-objects
 
 AM_CPPFLAGS = -I$(PYTHONINC) -I$(top_builddir) -I$(top_srcdir) \
-	      $(BUDDY_CPPFLAGS) -lpthread -latomic -DSWIG_TYPE_TABLE=spot
+	      $(BUDDY_CPPFLAGS) -lpthread -DSWIG_TYPE_TABLE=spot
 
 SWIGFLAGS = -c++ -python -py3 -O -MD
 
@@ -71,7 +71,7 @@ am__depfiles_remade = ./$(DEPDIR)/buddy_wrap.Plo \
 
 spot__impl_la_SOURCES = spot/impl_wrap.cxx
 spot__impl_la_LDFLAGS = -avoid-version -module $(SYMBOLIC_LDFLAGS)
-spot__impl_la_LIBADD = $(top_builddir)/spot/libspot.la -lpthread -latomic
+spot__impl_la_LIBADD = $(top_builddir)/spot/libspot.la -lpthread
 
 am__depfiles_remade += ./spot/$(DEPDIR)/impl_wrap.Pcxx
 @AMDEP_TRUE@@am__include@ @am__quote@./spot/$(DEPDIR)/impl_wrap.Pcxx@am__quote@ # am--include-marker
@@ -92,7 +92,7 @@ spot__ltsmin_la_SOURCES = spot/ltsmin_wrap.cxx
 spot__ltsmin_la_LDFLAGS = -avoid-version -module $(SYMBOLIC_LDFLAGS)
 spot__ltsmin_la_LIBADD = $(top_builddir)/spot/libspot.la \
                        $(top_builddir)/spot/ltsmin/libspotltsmin.la \
-					   -lpthread -latomic
+					   -lpthread
 
 am__depfiles_remade += ./spot/$(DEPDIR)/ltsmin_wrap.Pcxx
 @AMDEP_TRUE@@am__include@ @am__quote@./spot/$(DEPDIR)/ltsmin_wrap.Pcxx@am__quote@ # am--include-marker
@@ -111,7 +111,7 @@ spot__gen_la_SOURCES = spot/gen_wrap.cxx
 spot__gen_la_LDFLAGS = -avoid-version -module $(SYMBOLIC_LDFLAGS)
 spot__gen_la_LIBADD = $(top_builddir)/spot/libspot.la \
                        $(top_builddir)/spot/gen/libspotgen.la \
-					   -lpthread -latomic
+					   -lpthread
 
 am__depfiles_remade += ./spot/$(DEPDIR)/gen_wrap.Pcxx
 @AMDEP_TRUE@@am__include@ @am__quote@./spot/$(DEPDIR)/gen_wrap.Pcxx@am__quote@ # am--include-marker