FEXLoader: stderr on immediate failure

In the case that there is an immediate configuration failure. Use stderr specifically for outputting.
These errors won't be output typically because silent logging is enabled by default.
In the case of executable missing or rootfs configuration failure, print directly to stderr.
Previously it looked like FEX just exited for no reason.
We had multiple users encounter this and be confused

Source/Tests/FEXLoader.cpp

@@ -393,7 +393,7 @@ int main(int argc, char **argv, char **const envp) {
   if (!std::filesystem::exists(Program)) {
     // Early exit if the program passed in doesn't exist
     // Will prevent a crash later
-    LogMan::Msg::E("%s: command not found", Program.c_str());
+    fprintf(stderr, "%s: command not found\n", Program.c_str());
     return -ENOEXEC;
   }
 
@@ -409,7 +409,16 @@ int main(int argc, char **argv, char **const envp) {
 
   if (!Loader.ELFWasLoaded()) {
     // Loader couldn't load this program for some reason
-    LogMan::Msg::E("Invalid or Unsupported elf file.");
+    fprintf(stderr, "Invalid or Unsupported elf file.\n");
+#ifdef _M_ARM_64
+    fprintf(stderr, "This is likely due to a misconfigured x86-64 RootFS\n");
+    fprintf(stderr, "Current RootFS path set to '%s'\n", LDPath().c_str());
+    std::error_code ec;
+    if (LDPath().size() == 0 ||
+        std::filesystem::exists(LDPath(), ec) == false) {
+      fprintf(stderr, "RootFS path doesn't exist. This is required on AArch64 hosts\n");
+    }
+#endif
     return -ENOEXEC;
   }