Fix the builds with LLVM_TOOL_LLVM_DRIVER_BUILD enabled.

LLVM_ENABLE_EXPORTED_SYMBOLS_IN_EXECUTABLES is not completely
compatible with export_executable_symbols as the later will be ignored
if the previous is set to NO.

Fix the issue by passing if symbols need to be exported to
llvm_add_exectuable so the link flag can be determined directly
without calling export_executable_symbols_* later.

This reverts commit 5c56b46a32a8856a022a54291bc9294068f7ddbd. This break
lld build when using GENERATE_DRIVER.

`LLVM_ENABLE_EXPORTED_SYMBOLS_IN_EXECUTABLES` is not completely
compatible with `export_executable_symbols` as the later will be ignored
if the previous is set to NO.

 Fix the issue by passing if symbols need to be exported to
`llvm_add_exectuable` so the link flag can be determined directly
without calling `export_executable_symbols_*` later.

LLJIT needs access to symbols (e.g. llvm_orc_registerEHFrameSectionWrapper)
that will be defined in the executable when LLVM is linked statically.

Should fix https://github.com/llvm/llvm-project/issues/61712.

Clients don't care about linkage, and ExecutorAddr is much more ergonomic.

Now that we've moved to C++14, we no longer need the llvm::make_unique
implementation from STLExtras.h. This patch is a mechanical replacement
of (hopefully) all the llvm::make_unique instances across the monorepo.

llvm-svn: 369013

LLJITBuilder now has a setCompileFunctionCreator method which can be used to
construct a CompileFunction for the LLJIT instance being created. The motivating
use-case for this is supporting ObjectCaches, which can now be set up at
compile-function construction time. To demonstrate this an example project,
LLJITWithObjectCache, is included.

llvm-svn: 365671

A very minimal demo of how to use the LLJIT class, along the lines of the old
HowToUseJIT example.

llvm-svn: 361435