configure pthread support

Varnish is massively multithreaded, so all vmods must be thread-safe.

While it is possible to write thread-safe vmods without pthreads support,
some systems (like those of the Solaris-heritage) need additional compiler
flags for MT support (-D_REENTRANT -pthreads). To avoid weird potential
issues, we should, by default, include full MT support.

.gitignore

@@ -24,7 +24,11 @@ Makefile.in
 /ltmain.sh
 /missing
 /stamp-h1
-/m4/
+/m4/libtool.m4
+/m4/ltoptions.m4
+/m4/ltsugar.m4
+/m4/ltversion.m4
+/m4/lt~obsolete.m4
 
 /src/vcc_if.c
 /src/vcc_if.h

configure.ac

@@ -19,6 +19,12 @@ if test "x$ac_cv_prog_cc_c99" = xno; then
 fi
 AC_PROG_CPP
 
+AX_PTHREAD(,[AC_MSG_ERROR([Could not configure pthreads support])])
+
+LIBS="$PTHREAD_LIBS $LIBS"
+CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
+CC="$PTHREAD_CC"
+
 LT_INIT([disable-static])
 AC_PROG_INSTALL
 AC_PROG_LIBTOOL