6798822: (process) Non-portable use of isdigit in src/solaris/native/java/lang/UNIXProcess_md.c

Reviewed-by: alanb
Contributed-by: christos@zoulas.com

src/solaris/native/java/lang/UNIXProcess_md.c

@@ -259,6 +259,12 @@ Java_java_lang_UNIXProcess_waitForProcessExit(JNIEnv* env,
     }
 }
 
+static int
+isAsciiDigit(char c)
+{
+  return c >= '0' && c <= '9';
+}
+
 static int
 closeDescriptors(void)
 {
@@ -284,7 +290,7 @@ closeDescriptors(void)
      */
     while ((dirp = readdir64(dp)) != NULL) {
         int fd;
-        if (isdigit(dirp->d_name[0]) &&
+        if (isAsciiDigit(dirp->d_name[0]) &&
             (fd = strtol(dirp->d_name, NULL, 10)) >= from_fd + 2)
             close(fd);
     }