Instantiate Error in Target::GetEntryPointAddress() only when necessary

When `Target::GetEntryPointAddress()` calls `exe_module->GetObjectFile()->GetEntryPointAddress()`, and the returned
`entry_addr` is valid, it can immediately be returned.

However, just before that, an `llvm::Error` value has been setup, but in this case it is not consumed before returning, like is done further below in the function.

In https://bugs.freebsd.org/248745 we got a bug report for this, where a very simple test case aborts and dumps core:

```
* thread hfinkel#1, name = 'testcase', stop reason = breakpoint 1.1
    frame #0: 0x00000000002018d4 testcase`main(argc=1, argv=0x00007fffffffea18) at testcase.c:3:5
   1	int main(int argc, char *argv[])
   2	{
-> 3	    return 0;
   4	}
(lldb) p argc
Program aborted due to an unhandled Error:
Error value was Success. (Note: Success values must still be checked prior to being destroyed).

Thread 1 received signal SIGABRT, Aborted.
thr_kill () at thr_kill.S:3
3	thr_kill.S: No such file or directory.
(gdb) bt
#0  thr_kill () at thr_kill.S:3
hfinkel#1  0x00000008049a0004 in __raise (s=6) at /usr/src/lib/libc/gen/raise.c:52
hfinkel#2  0x0000000804916229 in abort () at /usr/src/lib/libc/stdlib/abort.c:67
hfinkel#3  0x000000000451b5f5 in fatalUncheckedError () at /usr/src/contrib/llvm-project/llvm/lib/Support/Error.cpp:112
hfinkel#4  0x00000000019cf008 in GetEntryPointAddress () at /usr/src/contrib/llvm-project/llvm/include/llvm/Support/Error.h:267
hfinkel#5  0x0000000001bccbd8 in ConstructorSetup () at /usr/src/contrib/llvm-project/lldb/source/Target/ThreadPlanCallFunction.cpp:67
hfinkel#6  0x0000000001bcd2c0 in ThreadPlanCallFunction () at /usr/src/contrib/llvm-project/lldb/source/Target/ThreadPlanCallFunction.cpp:114
hfinkel#7  0x00000000020076d4 in InferiorCallMmap () at /usr/src/contrib/llvm-project/lldb/source/Plugins/Process/Utility/InferiorCallPOSIX.cpp:97
hfinkel#8  0x0000000001f4be33 in DoAllocateMemory () at /usr/src/contrib/llvm-project/lldb/source/Plugins/Process/FreeBSD/ProcessFreeBSD.cpp:604
hfinkel#9  0x0000000001fe51b9 in AllocatePage () at /usr/src/contrib/llvm-project/lldb/source/Target/Memory.cpp:347
hfinkel#10 0x0000000001fe5385 in AllocateMemory () at /usr/src/contrib/llvm-project/lldb/source/Target/Memory.cpp:383
hfinkel#11 0x0000000001974da2 in AllocateMemory () at /usr/src/contrib/llvm-project/lldb/source/Target/Process.cpp:2301
hfinkel#12 CanJIT () at /usr/src/contrib/llvm-project/lldb/source/Target/Process.cpp:2331
hfinkel#13 0x0000000001a1bf3d in Evaluate () at /usr/src/contrib/llvm-project/lldb/source/Expression/UserExpression.cpp:190
hfinkel#14 0x00000000019ce7a2 in EvaluateExpression () at /usr/src/contrib/llvm-project/lldb/source/Target/Target.cpp:2372
hfinkel#15 0x0000000001ad784c in EvaluateExpression () at /usr/src/contrib/llvm-project/lldb/source/Commands/CommandObjectExpression.cpp:414
hfinkel#16 0x0000000001ad86ae in DoExecute () at /usr/src/contrib/llvm-project/lldb/source/Commands/CommandObjectExpression.cpp:646
hfinkel#17 0x0000000001a5e3ed in Execute () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandObject.cpp:1003
hfinkel#18 0x0000000001a6c4a3 in HandleCommand () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandInterpreter.cpp:1762
hfinkel#19 0x0000000001a6f98c in IOHandlerInputComplete () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandInterpreter.cpp:2760
hfinkel#20 0x0000000001a90b08 in Run () at /usr/src/contrib/llvm-project/lldb/source/Core/IOHandler.cpp:548
hfinkel#21 0x00000000019a6c6a in ExecuteIOHandlers () at /usr/src/contrib/llvm-project/lldb/source/Core/Debugger.cpp:903
hfinkel#22 0x0000000001a70337 in RunCommandInterpreter () at /usr/src/contrib/llvm-project/lldb/source/Interpreter/CommandInterpreter.cpp:2946
hfinkel#23 0x0000000001d9d812 in RunCommandInterpreter () at /usr/src/contrib/llvm-project/lldb/source/API/SBDebugger.cpp:1169
hfinkel#24 0x0000000001918be8 in MainLoop () at /usr/src/contrib/llvm-project/lldb/tools/driver/Driver.cpp:675
hfinkel#25 0x000000000191a114 in main () at /usr/src/contrib/llvm-project/lldb/tools/driver/Driver.cpp:890```

Fix the incorrect error catch by only instantiating an `Error` object if it is necessary.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D86355

(cherry picked from commit 1ce07cd)

lldb/source/Target/Target.cpp

@@ -2401,21 +2401,13 @@ lldb::addr_t Target::GetPersistentSymbol(ConstString name) {
 
 llvm::Expected<lldb_private::Address> Target::GetEntryPointAddress() {
   Module *exe_module = GetExecutableModulePointer();
-  llvm::Error error = llvm::Error::success();
-  assert(!error); // Check the success value when assertions are enabled.
 
-  if (!exe_module || !exe_module->GetObjectFile()) {
-    error = llvm::make_error<llvm::StringError>("No primary executable found",
-                                                llvm::inconvertibleErrorCode());
-  } else {
+  // Try to find the entry point address in the primary executable.
+  const bool has_primary_executable = exe_module && exe_module->GetObjectFile();
+  if (has_primary_executable) {
     Address entry_addr = exe_module->GetObjectFile()->GetEntryPointAddress();
     if (entry_addr.IsValid())
       return entry_addr;
-
-    error = llvm::make_error<llvm::StringError>(
-        "Could not find entry point address for executable module \"" +
-            exe_module->GetFileSpec().GetFilename().GetStringRef() + "\"",
-        llvm::inconvertibleErrorCode());
   }
 
   const ModuleList &modules = GetImages();
@@ -2426,14 +2418,21 @@ llvm::Expected<lldb_private::Address> Target::GetEntryPointAddress() {
       continue;
 
     Address entry_addr = module_sp->GetObjectFile()->GetEntryPointAddress();
-    if (entry_addr.IsValid()) {
-      // Discard the error.
-      llvm::consumeError(std::move(error));
+    if (entry_addr.IsValid())
       return entry_addr;
-    }
   }
 
-  return std::move(error);
+  // We haven't found the entry point address. Return an appropriate error.
+  if (!has_primary_executable)
+    return llvm::make_error<llvm::StringError>(
+        "No primary executable found and could not find entry point address in "
+        "any executable module",
+        llvm::inconvertibleErrorCode());
+
+  return llvm::make_error<llvm::StringError>(
+      "Could not find entry point address for primary executable module \"" +
+          exe_module->GetFileSpec().GetFilename().GetStringRef() + "\"",
+      llvm::inconvertibleErrorCode());
 }
 
 lldb::addr_t Target::GetCallableLoadAddress(lldb::addr_t load_addr,