Improve build.sh script

- Check for cmake, g++, and dotnet programs.
- Check for project.lock.json.
- Check that libpsl-native was compiled.

build.sh

@@ -1,15 +1,25 @@
 #!/usr/bin/env bash
 
-export BIN=$(pwd)/bin
-mkdir -p $BIN
+# Test for build dependencies
+hash cmake 2>/dev/null || { echo >&2 "No cmake, please run 'sudo apt-get install cmake'"; exit 1; }
+hash g++ 2>/dev/null || { echo >&2 "No g++, please run 'sudo apt-get install g++'"; exit 1; }
+hash dotnet 2>/dev/null || { echo >&2 "No dotnet, please visit https://dotnet.github.io/getting-started/"; exit 1; }
 
-# Build native components
+# Test for lock file
+test -r src/Microsoft.PowerShell.Linux.Host/project.lock.json || { echo >&2 "Please run 'dotnet restore' to download .NET Core packages"; exit 2; }
+
+# Ensure output directory is made
+BIN="$(pwd)/bin"
+mkdir -p "$BIN"
+
+# Build native library and deploy to bin
 pushd src/libpsl-native
 cmake -DCMAKE_BUILD_TYPE=Debug .
 make -j
 ctest -V
-cp src/libpsl-native.* $BIN
+test -r src/libpsl-native.* || { echo >&2 "Compilation of libpsl-native failed"; exit 3; }
+cp src/libpsl-native.* "$BIN"
 popd
 
-# Publish PowerShell
-dotnet publish --output $BIN --configuration Linux src/Microsoft.PowerShell.Linux.Host
+# Publish PowerShell to bin, with LINUX defined through a configuration
+dotnet publish --output "$BIN" --configuration Linux src/Microsoft.PowerShell.Linux.Host