[docs] fix output question (#177842)

See the code:
<img width="2631" height="1090" alt="image"
src="https://github.com/user-attachments/assets/dfe949b3-fbc6-4cd3-9e8d-5c0adbfcc67a"
/>
<img width="1751" height="577" alt="image"
src="https://github.com/user-attachments/assets/e3b78596-24b9-4bd5-b40d-a4154b2e6bb2"
/>


So the output is not the number, is the text "__anon_expr".

llvm/docs/tutorial/MyFirstLanguageFrontend/LangImpl03.rst

@@ -429,7 +429,7 @@ at the LLVM IR for simple functions. For example:
 
     ready> 4+5;
     Read top-level expression:
-    define double @0() {
+    define double @__anon_expr() {
     entry:
       ret double 9.000000e+00
     }
@@ -484,7 +484,7 @@ control flow to actually make recursion useful :).
 
     ready> cos(1.234);
     Read top-level expression:
-    define double @1() {
+    define double @__anon_expr() {
     entry:
       %calltmp = call double @cos(double 1.234000e+00)
       ret double %calltmp