Add system file for the new belize3

This adds belize3.sh, a system file for the newly-built belize3, using
the g++ compiler.

As a usage note, blitz requires python to build successfully.  As of
this writing, python is only available on belize3 with `module load
anaconda`.

systems/belize3.sh

+#!/bin/bash
+
+# System-specific settings for belize.math.uwaterloo.ca
+
+CC=gcc
+CXX=g++
+LD=mpic++
+
+# System-specific compiler flags
+SYSTEM_CFLAGS=
+SYSTEM_LDFLAGS=
+SYSTEM_CXXFLAGS=
+
+# Compiler flags for debugging
+DEBUG_CFLAGS="-g -DBZ_DEBUG"
+DEBUG_LDFLAGS=
+
+# Compiler flags for optimization
+OPTIM_CFLAGS="-O3 -ffast-math -march=native"
+OPTIM_LDFLAGS=$OPTIM_CFLAGS
+
+# Compiler flags for extra optimization, such as -ip -ipo on icc
+EXTRA_OPTIM_CFLAGS=
+EXTRA_OPTIM_LDFLAGS=
+
+# Library names/locations/flags for MPI-compilation.  This will
+# probably not be necessary on systems with a working mpicc
+# alias
+MPICXX=mpic++
+MPI_CFLAGS=
+MPI_LIB=
+MPI_LIBDIR=
+MPI_INCDIR=
+
+# Library names/locations for LAPACK
+LAPACK_LIB="-llapack -lblas"
+LAPACK_LIBDIR=
+LAPACK_INCDIR=
+
+# Library locations for blitz; leave blank to use system-installed
+# or compiled-with-this-package version
+BLITZ_LIBDIR=
+BLITZ_INCDIR=
+
+# Library locations for fftw
+FFTW_LIBDIR=
+FFTW_INCDIR=
+
+# Library locations for UMFPACK
+UMF_INCDIR=
+UMF_LIBDIR=
+
+# Location/library for BLAS
+BLAS_LIB="-lblas"
+BLAS_LIBDIR=
+BLAS_INCDIR=
+