The Makefile variable NATIVE defaults to 'on', in which case -march=native is used. This disables it.
Index: Makefile =================================================================== RCS file: /cvs/ports/math/ntl/Makefile,v retrieving revision 1.40 diff -u -p -r1.40 Makefile --- Makefile 21 Mar 2016 08:17:33 -0000 1.40 +++ Makefile 20 Apr 2016 03:49:47 -0000 @@ -3,6 +3,7 @@ COMMENT = Victor Shoup's Number Theory Library DISTNAME = ntl-9.7.0 +REVISION = 0 SHARED_LIBS = ntl 8.0 # 0.0 CATEGORIES = math @@ -25,7 +26,8 @@ CONFIGURE_STYLE = simple CONFIGURE_ARGS = CXX="${CXX}" CXXFLAGS="${CXXFLAGS}" \ NTL_GMP_LIP=on GMP_PREFIX="${LOCALBASE}" \ LIBntl_VERSION=${LIBntl_VERSION} \ - SHARED=on DEF_PREFIX="${LOCALBASE}" + SHARED=on DEF_PREFIX="${LOCALBASE}" \ + NATIVE=off WRKBUILD = ${WRKSRC}/src