Toolchain: Use set -o pipefail to the toolchain build script

Previously the buildstep function would obscure error codes because
the return value of the function was the exit code for the sed command
which caused us to continue execution even though one of the build
steps had failed.

With set -o pipefail the return value of the buildstep function is
the real command's exit code.

Toolchain/BuildIt.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
-set -e
+set -eo pipefail
 # This file will need to be run in bash, for now.
 
 
@@ -137,18 +137,24 @@ popd
 # === DOWNLOAD AND PATCH ===
 
 pushd "$DIR/Tarballs"
-    md5="$($MD5SUM $BINUTILS_PKG | cut -f1 -d' ')"
-    echo "bu md5='$md5'"
-    if [ ! -e $BINUTILS_PKG ] || [ "$md5" != ${BINUTILS_MD5SUM} ] ; then
+    md5=""
+    if [ -e "$BINUTILS_PKG" ]; then
+        md5="$($MD5SUM $BINUTILS_PKG | cut -f1 -d' ')"
+        echo "bu md5='$md5'"
+    fi
+    if [ "$md5" != ${BINUTILS_MD5SUM} ] ; then
         rm -f $BINUTILS_PKG
         curl -LO "$BINUTILS_BASE_URL/$BINUTILS_PKG"
     else
         echo "Skipped downloading binutils"
     fi
 
-    md5="$($MD5SUM ${GCC_PKG} | cut -f1 -d' ')"
-    echo "gc md5='$md5'"
-    if [ ! -e $GCC_PKG ] || [ "$md5" != ${GCC_MD5SUM} ] ; then
+    md5=""
+    if [ -e "$GCC_PKG" ]; then
+        md5="$($MD5SUM ${GCC_PKG} | cut -f1 -d' ')"
+        echo "gc md5='$md5'"
+    fi
+    if [ "$md5" != ${GCC_MD5SUM} ] ; then
         rm -f $GCC_PKG
         curl -LO "$GCC_BASE_URL/$GCC_NAME/$GCC_PKG"
     else