[LyX/master] Do not try to build an empty boost lib

[Georg Baum]

commit d67a8cb212dab9ac06fba93e2732af3fa081136a
Author: Georg Baum <b...@lyx.org>
Date:   Sat Jun 11 09:28:11 2016 +0200

    Do not try to build an empty boost lib
    
    This should fix a build failure on OS X:
    Making all in boost
      AR       liblyxboost.a
      ar: no archive members specified

diff --git a/3rdparty/Makefile.am b/3rdparty/Makefile.am
index c32db86..02dbfef 100644
--- a/3rdparty/Makefile.am
+++ b/3rdparty/Makefile.am
@@ -3,8 +3,11 @@ include $(top_srcdir)/config/common.am
 DIST_SUBDIRS = boost hunspell libiconv zlib
 
 if USE_INCLUDED_BOOST
+if LYX_USE_STD_REGEX
+else
 BOOST = boost
 endif
+endif
 
 if USE_INCLUDED_HUNSPELL
 HUNSPELL = hunspell
diff --git a/3rdparty/boost/Makefile.am b/3rdparty/boost/Makefile.am
index 54d34e3..7bd1ff0 100644
--- a/3rdparty/boost/Makefile.am
+++ b/3rdparty/boost/Makefile.am
@@ -12,10 +12,6 @@ EXTRA_DIST = boost \
 AM_CPPFLAGS += -DBOOST_USER_CONFIG="<config.h>" 
 AM_CPPFLAGS +=  $(BOOST_INCLUDES)
 
-if LYX_USE_STD_REGEX
-
-else
-
 # This version is more than three times faster than the one below
 
 if MONOLITHIC_BOOST
@@ -48,4 +44,3 @@ liblyxboost_a_SOURCES = \
 
 endif #MONOLITHIC_BOOST
 
-endif #LYX_USE_STD_REGEX