[LLD][ELF] Follow the common pattern in a message about an undefined vtable symbol.

[ikudrin]

Summary

In most cases, LLD prints its multiline diagnostic messages starting additional lines with ">>> ". That greatly helps external tools to parse the output, simplifying combining several lines of the log back into one message. The patch fixes the only message I found that does not follow the common pattern.

[grimar]

LGTM

[MaskRay]

LGTM.

lld/ELF/Relocations.cpp

if (const Symbol *corrected = getAlternativeSpelling<ELFT>(
             cast<Undefined>(sym), pre_hint, post_hint)) {
       msg += "\n>>> did you mean" + pre_hint + toString(*corrected) + post_hint;
       if (corrected->file)
         msg += "\n>>> defined in: " + toString(corrected->file);
     }
   }
 
   if (sym.getName().startswith("_ZTV"))
-    msg += "\nthe vtable symbol may be undefined because the class is missing "
-           "its key function (see https://lld.llvm.org/missingkeyfunction)";
+    msg +=
+        "\n>>> the vtable symbol may be undefined because the class is missing "
 
   if (undef.isWarning)
     warn(msg);
   else
     error(msg);
 }
 
 template <class ELFT> void reportUndefinedSymbols() {

lld/test/ELF/undef.s

 
 # CHECK:      error: undefined symbol: foo(int)
 # CHECK-NEXT: >>> referenced by undef.s
 # CHECK-NEXT: >>>               {{.*}}:(.text+0x10)
 
 # CHECK:      error: undefined symbol: vtable for Foo 
 # CHECK-NEXT: >>> referenced by undef.s
 # CHECK-NEXT: >>>               {{.*}}:(.text+0x15)
-# CHECK-NEXT: the vtable symbol may be undefined because the class is missing its key function (see https://lld.llvm.org/missingkeyfunction)
+# CHECK-NEXT: >>> the vtable symbol may be undefined because the class is missing its key function (see https://lld.llvm.org/missingkeyfunction)
 
 # Check that this symbol isn't demangled
 
 # CHECK:      error: undefined symbol: __Z3fooi
 # CHECK-NEXT: >>> referenced by undef.s
 # CHECK-NEXT: >>>               {{.*}}:(.text+0x1A)
 
 # CHECK:      error: undefined symbol: zed2