mbdyn: try setting -std=c++11 for C++11 errors

science/mbdyn/Portfile

@@ -23,10 +23,6 @@ checksums           rmd160  d4d4371936071a9d965f752660b5ba8f4ddcadcc \
 compiler.cxx_standard       2011
 compiler.require_fortran    yes
 
-# Teach glibtool about -stdlib=libc++
-use_autoreconf      yes
-autoreconf.args     -fvi
-
 depends_build       port:pkgconfig
 
 depends_lib         port:gcc15 \
@@ -46,6 +42,9 @@ configure.args      --with-blas=blas \
                     --with-mpi=no \
                     --with-metis=yes
 
+configure.cxxflags-append \
+                    -std=c++11
+
 # workaround for Type mismatch in argument 't' at (1); passed REAL(4) to INTEGER(4)
 # See FreeBSD Makefile
 configure.env       FFLAGS=-fallow-argument-mismatch