TSCBasic: properly track abnormal exits on Windows

The process handling did not properly account for abnormal process
termination.  Unlike Unix platforms, Windows does not have a concept of
signals.  However, a process may be terminated abnormally by means of an
exception.  The exception code is then transliterated into the exit code
for the process.  In most circumstances, the exit code for the process
in such a case is either a `NTSTATUS` or `HRESULT`.  Accordingly, the
way to detect the exception is to check the severity code of the
exception.  The `HRESULT` and `NTSTATUS` codes are similarly structured:

~~~
                     1                     2                  3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|R|C|N|X|F A C I L I T Y      |C O D E                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
S: Severity; If set, indicates a failure result. If clear, indicates a success result.
R: Reserved; If N is clear, this bit MUST be set to 0.
C: Customer; If set, indicates that this a customer defined error code.
N: If set, indicates that the error code is a NTSTATUS value.
X: Reserved; MBZ
Facility: An indicator of the source of the error.
Code: The remainder of the error code.
~~~

We would previously only check for the top nibble being 0xC or 0xE.
However, a 0x8 value is also permissible and indicates a failure.  Plumb
this through as an abnormal exit with the specified exception code.

Author: compnerd

Sources/TSCBasic/Process.swift

@@ -34,7 +34,10 @@ public struct ProcessResult: CustomStringConvertible {
     public enum ExitStatus: Equatable {
         /// The process was terminated normally with a exit code.
         case terminated(code: Int32)
-#if !os(Windows)
+#if os(Windows)
+        /// The process was terminated abnormally.
+        case abnormal(exception: UInt32)
+#else
         /// The process was terminated due to a signal.
         case signalled(signal: Int32)
 #endif
@@ -64,12 +67,17 @@ public struct ProcessResult: CustomStringConvertible {
         arguments: [String],
         environment: [String: String],
         exitStatusCode: Int32,
+        normal: Bool,
         output: Result<[UInt8], Swift.Error>,
         stderrOutput: Result<[UInt8], Swift.Error>
     ) {
         let exitStatus: ExitStatus
       #if os(Windows)
-        exitStatus = .terminated(code: exitStatusCode)
+        if normal {
+            exitStatus = .terminated(code: exitStatusCode)
+        } else {
+            exitStatus = .abnormal(exception: exitStatusCode)
+        }
       #else
         if WIFSIGNALED(exitStatusCode) {
             exitStatus = .signalled(signal: WTERMSIG(exitStatusCode))
@@ -742,6 +750,7 @@ public final class Process {
                 arguments: arguments,
                 environment: environment,
                 exitStatusCode: exitStatusCode,
+                normal: p.terminationReason == .exit,
                 output: stdoutResult,
                 stderrOutput: stderrResult
             )
@@ -970,7 +979,10 @@ extension ProcessResult.Error: CustomStringConvertible {
             switch result.exitStatus {
             case .terminated(let code):
                 stream <<< "terminated(\(code)): "
-#if !os(Windows)
+#if os(Windows)
+            case .abnormal(let exception):
+                stream <<< "abnormal(\(exception)): "
+#else
             case .signalled(let signal):
                 stream <<< "signalled(\(signal)): "
 #endif