https://bugs.gentoo.org/548310

apply boost.m4 updates to fix building w/gcc-5

--- a/configure

+++ b/configure

@@ -17481,8 +17481,10 @@

 boost-lib-version = BOOST_LIB_VERSION

 _ACEOF

 if (eval "$ac_cpp conftest.$ac_ext") 2>&5 |

+  grep -v '#' |

   tr -d '\r' |

-  $SED -n -e "/^boost-lib-version = /{s///;s/\"//g;p;q;}" >conftest.i 2>&1; then :

+  tr -s '\n' ' ' |

+  $SED -n -e "/^boost-lib-version = /{s///;s/[\" ]//g;p;q;}" >conftest.i 2>&1; then :

   boost_cv_lib_version=`cat conftest.i`

 fi

 rm -rf conftest*