GP-0: Fix exit code for "not found" (after GP-994)

Ghidra/Debug/Debugger-agent-gdb/src/main/java/agent/gdb/pty/linux/LinuxPtySessionLeader.java

@@ -79,7 +79,7 @@ public class LinuxPtySessionLeader {
 				}
 			}
 			System.err.println("Could not execute " + subArgs.get(0) + ": " + t.getMessage());
-			System.exit(-1);
+			System.exit(127);
 		}
 	}
 }

Ghidra/Debug/Debugger-agent-gdb/src/test/java/agent/gdb/pty/linux/LinuxPtyTest.java

@@ -84,10 +84,9 @@ public class LinuxPtyTest extends AbstractPtyTest {
 			PtySession dies =
 				pty.getChild().session(new String[] { "thisHadBetterNotExist" }, null);
 			/**
-			 * NOTE: Java subprocess dies with code 1 on unhandled exception. TODO: Is there a nice
-			 * way to distinguish whether the code is from java or the execed image?
+			 * Choice of 127 is based on bash setting "exit code" to 127 for "command not found"
 			 */
-			assertEquals(1, dies.waitExited());
+			assertEquals(127, dies.waitExited());
 		}
 	}