[lldb] Treat address found via function name as a callable address (#151973)

I discovered this building the lldb test suite with `-mthumb` set, so
that all test programs are purely Arm Thumb code.

When C++ expressions did a function lookup, they took a different path
from C programs. That path happened to land on the line that I've
changed. Where we try to look something up as a function, but don't then
resolve the address as if it's a callable.

With Thumb, if you do the non-callable lookup, the bottom bit won't be
set. This means when lldb's expression wrapper function branches into
the found function, it'll be in Arm mode trying to execute Thumb code.

Thumb is the only instance where you'd notice this. Aside from maybe
MicroMIPS or MIPS16 perhaps but I expect that there are 0 users of that
and lldb.

I have added a new test case that will simulate this situation in
"normal" Arm builds so that it will get run on Linaro's buildbot.

This change also fixes the following existing tests when `-mthumb` is
used:
```
  lldb-api :: commands/expression/anonymous-struct/TestCallUserAnonTypedef.py
  lldb-api :: commands/expression/argument_passing_restrictions/TestArgumentPassingRestrictions.py
  lldb-api :: commands/expression/call-function/TestCallStopAndContinue.py
  lldb-api :: commands/expression/call-function/TestCallUserDefinedFunction.py
  lldb-api :: commands/expression/char/TestExprsChar.py
  lldb-api :: commands/expression/class_template_specialization_empty_pack/TestClassTemplateSpecializationParametersHandling.py
  lldb-api :: commands/expression/context-object/TestContextObject.py
  lldb-api :: commands/expression/formatters/TestFormatters.py
  lldb-api :: commands/expression/import_base_class_when_class_has_derived_member/TestImportBaseClassWhenClassHasDerivedMember.py
  lldb-api :: commands/expression/inline-namespace/TestInlineNamespace.py
  lldb-api :: commands/expression/namespace-alias/TestInlineNamespaceAlias.py
  lldb-api :: commands/expression/no-deadlock/TestExprDoesntBlock.py
  lldb-api :: commands/expression/pr35310/TestExprsBug35310.py
  lldb-api :: commands/expression/static-initializers/TestStaticInitializers.py
  lldb-api :: commands/expression/test/TestExprs.py
  lldb-api :: commands/expression/timeout/TestCallWithTimeout.py
  lldb-api :: commands/expression/top-level/TestTopLevelExprs.py
  lldb-api :: commands/expression/unwind_expression/TestUnwindExpression.py
  lldb-api :: commands/expression/xvalue/TestXValuePrinting.py
  lldb-api :: functionalities/thread/main_thread_exit/TestMainThreadExit.py
  lldb-api :: lang/cpp/call-function/TestCallCPPFunction.py
  lldb-api :: lang/cpp/chained-calls/TestCppChainedCalls.py
  lldb-api :: lang/cpp/class-template-parameter-pack/TestClassTemplateParameterPack.py
  lldb-api :: lang/cpp/constructors/TestCppConstructors.py
  lldb-api :: lang/cpp/function-qualifiers/TestCppFunctionQualifiers.py
  lldb-api :: lang/cpp/function-ref-qualifiers/TestCppFunctionRefQualifiers.py
  lldb-api :: lang/cpp/global_operators/TestCppGlobalOperators.py
  lldb-api :: lang/cpp/llvm-style/TestLLVMStyle.py
  lldb-api :: lang/cpp/multiple-inheritance/TestCppMultipleInheritance.py
  lldb-api :: lang/cpp/namespace/TestNamespace.py
  lldb-api :: lang/cpp/namespace/TestNamespaceLookup.py
  lldb-api :: lang/cpp/namespace_conflicts/TestNamespaceConflicts.py
  lldb-api :: lang/cpp/operators/TestCppOperators.py
  lldb-api :: lang/cpp/overloaded-functions/TestOverloadedFunctions.py
  lldb-api :: lang/cpp/rvalue-references/TestRvalueReferences.py
  lldb-api :: lang/cpp/static_methods/TestCPPStaticMethods.py
  lldb-api :: lang/cpp/template/TestTemplateArgs.py
  lldb-api :: python_api/thread/TestThreadAPI.py
```

There are other failures that are due to different problems, and this
change does not make those worse.

(I have no plans to run the test suite with `-mthumb` regularly, I just
did it to test some other refactoring)