prefer -pthread to -lpthread

* configure.ac,
spot/ltsmin/Makefile.am,
tests/Makefile.am: Here.

configure.ac

@@ -77,8 +77,6 @@ fi
 # Activate C11 for gnulib tests
 AX_CHECK_COMPILE_FLAG([-std=c11], [CFLAGS="$CFLAGS -std=c11"])
 
-AX_CHECK_COMPILE_FLAG([-lpthread], [CFLAGS="$CFLAGS -lpthread"])
-
 gl_INIT
 
 # Use -Werror since using -fvisibility under MinGW is only a warning.

spot/ltsmin/Makefile.am

@@ -20,7 +20,7 @@
 AM_CPPFLAGS = -I$(top_builddir) -I$(top_srcdir) \
               $(BUDDY_CPPFLAGS) $(LTDLINCL) \
               -I$(top_builddir)/lib -I$(top_srcdir)/lib
-AM_CXXFLAGS = $(WARNING_CXXFLAGS)
+AM_CXXFLAGS = $(WARNING_CXXFLAGS) -pthread
 
 ltsmindir = $(pkgincludedir)/ltsmin
 

tests/Makefile.am

@@ -460,6 +460,7 @@ if USE_LTSMIN
 check_PROGRAMS += ltsmin/modelcheck
 ltsmin_modelcheck_CPPFLAGS = -I$(top_builddir) -I$(top_srcdir) \
 	$(BUDDY_CPPFLAGS) \-I$(top_builddir)/lib -I$(top_srcdir)/lib
+ltsmin_modelcheck_CXXFLAGS = $(CXXFLAGS) -pthread
 ltsmin_modelcheck_SOURCES = ltsmin/modelcheck.cc
 ltsmin_modelcheck_LDADD =  \
   $(top_builddir)/bin/libcommon.a		\