Added missing m4 file ax_boost_chrono

Summary:
To avoid error while running ./configure command:
 ./configure: line 18976: AX_BOOST_CHRONO: command not found

Besides in my Fedora 23 the following error ocurred when not linked with -lboost_chrono running 'make check':
/usr/bin/ld: SynchronizedTest.o: undefined reference to symbol 'boost::chrono::steady_clock::now()''
/usr/lib64/libboost_chrono.so.1.58.0: error adding symbols: DSO missing from command line
Closes https://github.com/facebook/folly/pull/426

Differential Revision: D3457939

Pulled By: elliottneilclark

fbshipit-source-id: ec7a8d30d4812f197e2813e611cde0e33eab680a

folly/m4/ax_boost_chrono.m4

+# ===========================================================================
+#      http://www.gnu.org/software/autoconf-archive/ax_boost_chrono.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_BOOST_CHRONO
+#
+# DESCRIPTION
+#
+#   Test for System library from the Boost C++ libraries. The macro requires
+#   a preceding call to AX_BOOST_BASE. Further documentation is available at
+#   <http://randspringer.de/boost/index.html>.
+#
+#   This macro calls:
+#
+#     AC_SUBST(BOOST_CHRONO_LIB)
+#
+#   And sets:
+#
+#     HAVE_BOOST_CHRONO
+#
+# LICENSE
+#
+#   Copyright (c) 2012 Xiyue Deng <manphiz@gmail.com>
+#
+#   Copying and distribution of this file, with or without modification, are
+#   permitted in any medium without royalty provided the copyright notice
+#   and this notice are preserved. This file is offered as-is, without any
+#   warranty.
+
+#serial 1
+
+AC_DEFUN([AX_BOOST_CHRONO],
+[
+	AC_ARG_WITH([boost-chrono],
+	AS_HELP_STRING([--with-boost-chrono@<:@=special-lib@:>@],
+                   [use the Chrono library from boost - it is possible to specify a certain library for the linker
+                        e.g. --with-boost-chrono=boost_chrono-gcc-mt ]),
+        [
+        if test "$withval" = "no"; then
+			want_boost="no"
+        elif test "$withval" = "yes"; then
+            want_boost="yes"
+            ax_boost_user_chrono_lib=""
+        else
+		    want_boost="yes"
+		ax_boost_user_chrono_lib="$withval"
+		fi
+        ],
+        [want_boost="yes"]
+	)
+
+	if test "x$want_boost" = "xyes"; then
+        AC_REQUIRE([AC_PROG_CC])
+        AC_REQUIRE([AC_CANONICAL_BUILD])
+		CPPFLAGS_SAVED="$CPPFLAGS"
+		CPPFLAGS="$CPPFLAGS $BOOST_CPPFLAGS"
+		export CPPFLAGS
+
+		LDFLAGS_SAVED="$LDFLAGS"
+		LDFLAGS="$LDFLAGS $BOOST_LDFLAGS"
+		export LDFLAGS
+
+        AC_CACHE_CHECK(whether the Boost::Chrono library is available,
+					   ax_cv_boost_chrono,
+        [AC_LANG_PUSH([C++])
+			 CXXFLAGS_SAVE=$CXXFLAGS
+
+			 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[@%:@include <boost/chrono.hpp>]],
+                                   [[boost::chrono::system_clock::time_point time;]])],
+                   ax_cv_boost_chrono=yes, ax_cv_boost_chrono=no)
+			 CXXFLAGS=$CXXFLAGS_SAVE
+             AC_LANG_POP([C++])
+		])
+		if test "x$ax_cv_boost_chrono" = "xyes"; then
+			AC_SUBST(BOOST_CPPFLAGS)
+
+			AC_DEFINE(HAVE_BOOST_CHRONO,,[define if the Boost::Chrono library is available])
+            BOOSTLIBDIR=`echo $BOOST_LDFLAGS | sed -e 's/@<:@^\/@:>@*//'`
+
+			LDFLAGS_SAVE=$LDFLAGS
+            if test "x$ax_boost_user_chrono_lib" = "x"; then
+                for libextension in `ls $BOOSTLIBDIR/libboost_chrono*.so* $BOOSTLIBDIR/libboost_chrono*.dylib* $BOOSTLIBDIR/libboost_chrono*.a* 2>/dev/null | sed 's,.*/,,' | sed -e 's;^lib\(boost_chrono.*\)\.so.*$;\1;' -e 's;^lib\(boost_chrono.*\)\.dylib.*$;\1;' -e 's;^lib\(boost_chrono.*\)\.a.*$;\1;'` ; do
+                     ax_lib=${libextension}
+				    AC_CHECK_LIB($ax_lib, exit,
+                                 [BOOST_CHRONO_LIB="-l$ax_lib"; AC_SUBST(BOOST_CHRONO_LIB) link_chrono="yes"; break],
+                                 [link_chrono="no"])
+				done
+                if test "x$link_chrono" != "xyes"; then
+                for libextension in `ls $BOOSTLIBDIR/boost_chrono*.dll* $BOOSTLIBDIR/boost_chrono*.a* 2>/dev/null | sed 's,.*/,,' | sed -e 's;^\(boost_chrono.*\)\.dll.*$;\1;' -e 's;^\(boost_chrono.*\)\.a.*$;\1;'` ; do
+                     ax_lib=${libextension}
+				    AC_CHECK_LIB($ax_lib, exit,
+                                 [BOOST_CHRONO_LIB="-l$ax_lib"; AC_SUBST(BOOST_CHRONO_LIB) link_chrono="yes"; break],
+                                 [link_chrono="no"])
+				done
+                fi
+
+            else
+               for ax_lib in $ax_boost_user_chrono_lib boost_chrono-$ax_boost_user_chrono_lib; do
+				      AC_CHECK_LIB($ax_lib, exit,
+                                   [BOOST_CHRONO_LIB="-l$ax_lib"; AC_SUBST(BOOST_CHRONO_LIB) link_chrono="yes"; break],
+                                   [link_chrono="no"])
+                  done
+
+            fi
+            if test "x$ax_lib" = "x"; then
+                AC_MSG_ERROR(Could not find a version of the library!)
+            fi
+			if test "x$link_chrono" = "xno"; then
+				AC_MSG_ERROR(Could not link against $ax_lib !)
+			fi
+		fi
+
+		CPPFLAGS="$CPPFLAGS_SAVED"
+	LDFLAGS="$LDFLAGS_SAVED"
+	fi
+])