boost: use c++11 for building

Closes: https://trac.macports.org/ticket/55926

devel/boost/Portfile

@@ -3,11 +3,12 @@
 PortSystem      1.0
 PortGroup       compiler_blacklist_versions 1.0
 PortGroup       mpi 1.0
+PortGroup       cxx11 1.1
 
 name            boost
 
 version         1.66.0
-revision        1
+revision        2
 checksums       rmd160  ee5dafdfa49adf50a5333cef1f55dac4f70b4c14 \
                 sha256  5721818253e6a0989583192f96782c4a98eb6204965316df9f5ad75819225ca9 \
                 size    85995778
@@ -88,6 +89,13 @@ compiler.blacklist {clang < 421} *llvm-gcc-4.2 *gcc-4.0 gcc-3.3
 compilers.choose   cc cxx
 mpi.setup          -gcc -dragonegg
 
+# NOTE: although technically Boost does not require C++11 compliance
+# for building, doing so allows for building on more OSs than without.
+# Further: Building Boost using C++11 compliance does not seem to then
+# require ports depending on Boost to also require C++11 compliance,
+# and requiring it does make such building easier for those ports.
+configure.cxxflags-append -std=gnu++11
+
 # It turns out that ccache and distcc can produce boost libraries that, although they
 # compile without warning, have all sorts of runtime errors especially with pointer corruption.
 # Since most people will now use MacPorts' pre-compiled boost, this should not be a problem.