improve IOException message in the case of a Runtime.exec() failure

We now properly forward the errno value from the child when execvp()
fails, which the parent then uses to for the errno message as well as
including the failed command's name in the message.

classpath/java-lang.cpp

@@ -411,8 +411,8 @@ Java_java_lang_Runtime_exec(JNIEnv* e, jclass,
     execvp(argv[0], argv);
     
     // Error if here
-    char c = errno;
+    int val = errno;
-    ssize_t rv UNUSED = write(msg[1], &c, 1);
+    ssize_t rv UNUSED = write(msg[1], &val, sizeof(val));
     exit(127);
   } break;
     
@@ -425,12 +425,13 @@ Java_java_lang_Runtime_exec(JNIEnv* e, jclass,
     safeClose(err[1]);
     safeClose(msg[1]);
       
-    char c;
+    int val;
-    int r = read(msg[0], &c, 1);
+    int r = read(msg[0], &val, sizeof(val));
     if(r == -1) {
       throwNewErrno(e, "java/io/IOException");
       return;
     } else if(r) {
+      errno = val;
       throwNewErrno(e, "java/io/IOException");
       return;
     }

classpath/java/lang/Runtime.java

@@ -103,7 +103,8 @@ public class Runtime {
 
     if (exception[0] != null) {
       if (exception[0] instanceof IOException) {
-        throw new IOException(exception[0]);
+        String message = "Failed to run \"" + command[0] + "\": " + exception[0].getMessage();
+        throw new IOException(message);
       } else {
         throw new RuntimeException(exception[0]);
       }