Use shasum instead of sha256sum to be more portable

shasum exists on at least OS X and Linux
diff --git a/doit b/doit
index 800a691..2cf5119 100755
--- a/doit
+++ b/doit
@@ -66,7 +66,7 @@
     fi
 
     echo "checking $TARFILE integrity"
-    if [ "$(sha256sum "$ARCHIVES/$TARFILE" | cut -f1 -d' ')" != "$HASH" ]; then
+    if [ "$(shasum -a 256 -b "$ARCHIVES/$TARFILE" | cut -f1 -d' ')" != "$HASH" ]; then
       log echo "$TARFILE failed integrity check"
       exit 1
     fi
diff --git a/updatetoolvers b/updatetoolvers
index ec3f8a6..6cad08a 100755
--- a/updatetoolvers
+++ b/updatetoolvers
@@ -39,12 +39,12 @@
 fetch_and_verify "$GNU_MIRROR/mpc/" "mpc-$MPCVER.tar.gz"
 fetch_and_verify "$GNU_MIRROR/gmp/" "gmp-$GMPVER.tar.bz2"
 
-BINHASH=$(sha256sum "$ARCHIVES/binutils-$BINVER.tar.bz2" | cut -f1 -d' ')
-GCCHASH=$(sha256sum "$ARCHIVES/gcc-$GCCVER.tar.bz2" | cut -f1 -d' ')
-GDBHASH=$(sha256sum "$ARCHIVES/gdb-$GDBVER.tar.xz" | cut -f1 -d' ')
-MPFRHASH=$(sha256sum "$ARCHIVES/mpfr-$MPFRVER.tar.bz2" | cut -f1 -d' ')
-MPCHASH=$(sha256sum "$ARCHIVES/mpc-$MPCVER.tar.gz" | cut -f1 -d' ')
-GMPHASH=$(sha256sum "$ARCHIVES/gmp-$GMPVER.tar.bz2" | cut -f1 -d' ')
+BINHASH=$(shasum -a 256 -b "$ARCHIVES/binutils-$BINVER.tar.bz2" | cut -f1 -d' ')
+GCCHASH=$(shasum -a 256 -b "$ARCHIVES/gcc-$GCCVER.tar.bz2" | cut -f1 -d' ')
+GDBHASH=$(shasum -a 256 -b "$ARCHIVES/gdb-$GDBVER.tar.xz" | cut -f1 -d' ')
+MPFRHASH=$(shasum -a 256 -b "$ARCHIVES/mpfr-$MPFRVER.tar.bz2" | cut -f1 -d' ')
+MPCHASH=$(shasum -a 256 -b "$ARCHIVES/mpc-$MPCVER.tar.gz" | cut -f1 -d' ')
+GMPHASH=$(shasum -a 256 -b "$ARCHIVES/gmp-$GMPVER.tar.bz2" | cut -f1 -d' ')
 
 tmp=$(mktemp)
 echo "# Rerun updatetoolvers after modifying this file" > "$tmp"