Minor build improvements.

The build_linux.sh scripts stops when encountering an error
and reports what it is doing.

Directories constructed temporarily during the build
ignored by git, as we do not want to version those.

/usr/bin has become the official dwelling place of bash.

.gitignore

@@ -0,0 +1,3 @@
+LPCNet
+build_linux
+codec2

build_linux.sh

@@ -1,9 +1,12 @@
-#!/bin/bash
+#!/usr/bin/bash
 # build_ubuntu.sh
 #
 # Build script for Ubuntu and Fedora Linux, git pulls codec2 and
 # lpcnet repos so they are available for parallel development.
 
+# Echo what you are doing, and fail if any of the steps fail:
+set -x -e
+
 export FREEDVGUIDIR=${PWD}
 export CODEC2DIR=$FREEDVGUIDIR/codec2
 export LPCNETDIR=$FREEDVGUIDIR/LPCNet