Fix Windows default search paths

Author: stevapple

Sources/TSCBasic/Process.swift

@@ -358,18 +358,15 @@ public final class Process {
             if GetSystemDirectoryW(&buffer, .init(buffer.count)) > 0 {
                 searchPaths.append(AbsolutePath(String(decodingCString: buffer, as: UTF16.self)))
             }
-            // The 16-bit Windows system directory
-            if let systemDrive = ProcessEnv.vars["systemdrive"],
-               let systemPath = try? AbsolutePath(validating: "\(systemDrive))\\System") {
-                searchPaths.append(systemPath)
-            }
-            // The Windows directory
             if GetWindowsDirectoryW(&buffer, .init(buffer.count)) > 0 {
-                searchPaths.append(AbsolutePath(String(decodingCString: buffer, as: UTF16.self)))
+                let windowsDirectory = String(decodingCString: buffer, as: UTF16.self)
+                // The 16-bit Windows system directory
+                searchPaths.append(AbsolutePath("\(windowsDirectory)\\System"))
+                // The Windows directory
+                searchPaths.append(AbsolutePath(windowsDirectory))
             }
 #endif
             searchPaths.append(contentsOf: envSearchPaths)
-            // Lookup and cache the executable path.
             let value = lookupExecutablePath(
                 filename: program,
                 currentWorkingDirectory: cwdOpt,