boost 1.78.0 (and many previous versions?) do not support the documented GCC versions.. "This library now requires a C++11 or later compiler" should minimal requirements be updated?

Cross-filed with https://github.com/boostorg/multiprecision/issues/420

As documented on the [release notes](https://www.boost.org/users/history/version_1_78_0.html)

"""
Boost's primary test compilers are:

Linux:
...
GCC, C++11: 4.7.3, 4.8.5, 11
"""

But this does play out in practice.. compiling with GCC4.7.3, GCC4.8.5 with -std=c++ fails. Should the release notes change?

boost/1.78.0/boost/multiprecision/detail/number_base.hpp:36:2: error: #error "This library now requires a C++11 or later compiler - this message was generated as a result of BOOST_NO_CXX11_HDR_TYPE_TRAITS being set"

/usr/bin/gcc/4.7.3/bin/g++ -c -std=c++11 -fPIC -DBOOST_PP_VARIADICS test.cpp

from test.cpp:13:
/usr/boost/1.78.0/boost/multiprecision/detail/number_base.hpp:36:2: error: #error "This library now requires a C++11 or later compiler - this message was generated as a result of BOOST_NO_CXX11_HDR_TYPE_TRAITS being set"
/usr/boost/1.78.0/boost/multiprecision/detail/number_base.hpp:48:2: error: #error "This library now requires a C++11 or later compiler - this message was generated as a result of BOOST_NO_CXX11_REF_QUALIFIERS being set"
/usr/boost/1.78.0/boost/multiprecision/detail/number_base.hpp:72:2: error: #error "This library now requires a C++11 or later compiler - this message was generated as a result of BOOST_NO_CXX11_REF_QUALIFIERS being set"
/usr/boost/1.78.0/boost/multiprecision/detail/number_base.hpp:92:0: warning: ignoring #pragma GCC warning [-Wunknown-pragmas]
In file included from /usr/boost/1.78.0/boost/multiprecision/cpp_int.hpp:14:0,
from /usr/boost/1.78.0/boost/multiprecision/integer.hpp:10,
from test.cpp:13:

The same happens with GCC 4.8.5 ... the lowest GCC that works for me is 5.3.0