Add missing pthread dependency.

Makefile.am

@@ -2,6 +2,7 @@ warningflags = -Wall -Wextra -Wno-unused-parameter -Wno-unused-function -Wno-ign
 commoncflags = -O3 -fvisibility=hidden $(warningflags) -I$(srcdir)/include $(DEBUGCFLAGS) $(MFLAGS) $(UNICODECFLAGS) $(STACKREALIGN)
 AM_CXXFLAGS = -std=c++11 $(commoncflags)
 AM_CFLAGS = -std=c99 $(commoncflags)
+ACLOCAL_AMFLAGS = -I m4
 
 
 
@@ -80,8 +81,8 @@ pkginclude_HEADERS = include/VapourSynth.h \
 pkgconfig_DATA += pc/vapoursynth.pc
 
 libvapoursynth_la_LDFLAGS = -no-undefined -avoid-version $(UNDEFINEDLDFLAGS)
-libvapoursynth_la_CPPFLAGS = $(ZIMG_CFLAGS) -DVS_PATH_PLUGINDIR='"$(PLUGINDIR)"'
-libvapoursynth_la_LIBADD = $(ZIMG_LIBS) $(DLOPENLIB) libexprfilter.la
+libvapoursynth_la_CPPFLAGS = $(PTHREAD_CFLAGS) $(ZIMG_CFLAGS) -DVS_PATH_PLUGINDIR='"$(PLUGINDIR)"'
+libvapoursynth_la_LIBADD = $(PTHREAD_LIBS) $(ZIMG_LIBS) $(DLOPENLIB) libexprfilter.la
 
 
 if X86ASM

configure.ac

@@ -11,9 +11,11 @@ LT_INIT([win32-dll])
 AC_PROG_CC
 AC_PROG_CXX
 
+AC_CONFIG_MACRO_DIRS([m4])
 
 AC_SYS_LARGEFILE
 AC_FUNC_FSEEKO
+AX_PTHREAD
 
 
 AC_ARG_ENABLE([debug], AS_HELP_STRING([--enable-debug], [Enable compilation options required for debugging. (default=no)]))