[lldb] Add -Wl,-rpath to make tests run with fresh built libc++

[lldb] Add -Wl,-rpath to make tests run with fresh built libc++

On my Debian machine, system libc++/libc++abi is not installed (`libc++1-9 libc++abi-9`),
21 check-lldb-api tests fail because -stdlib=libc++ linked executables cannot
find runtime libc++.so.1 at runtime.

Use the `-Wl,-rpath,$(LLVM_LIBS_DIR)` mechanism in
`packages/Python/lldbsuite/test/make/Makefile.rules` (D58630 for NetBSD) to
allow such tests compile/link with fresh libc++ built beside lldb.
(A system libc++.so.1 is not guaranteed to match fresh libc++ header files.)

Some tweaks to the existing NetBSD rule when generalizing:

* Drop `-L$(LLVM_LIBS_DIR)` since Clang driver adds it correctly.
* Add `-stdlib=libc++` only for `USE_LIBCPP`.

Also, drop `-isystem /usr/include/c++/v1` introduced in D9426. It is not needed
by Clang driver. GCC using libc++ requires more setup.

I don't find any test needing `-Wl,-rpath` in `test/Shell/helper/{build,toolchain}.py` (D58630 for NetBSD added them).

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D94888