Add a simple ELF binary called _test.o to the test fs.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/5b10846bed5

Kernel/Userspace.cpp

@@ -4,6 +4,14 @@
 
 namespace Userspace {
 
+int strlen(const char* str)
+{
+    int len = 0;
+    while (*(str++))
+        ++len;
+    return len;
+}
+
 int open(const char* path)
 {
     return DO_SYSCALL_A2(Syscall::PosixOpen, path, strlen(path));

Kernel/_test.cpp

@@ -0,0 +1,12 @@
+#include "Userspace.cpp"
+
+using namespace Userspace;
+
+int elf_entry()
+{
+    int fd = open("/Banner.txt");
+    char buf[2048];
+    int nread = read(fd, buf, sizeof(buf));
+    buf[nread] = '\0';
+    return 0;
+}