[libunwind] Fix path to libunwind for per-target-runtime-dir builds

[ldionne]

Summary

We recently introduced a from-scratch config to run the libunwind tests.
However, that config was always looking for libunwind in <install>/lib,
and never in <install>/<target>/lib, which is necessary for tests to
work when the per-target-runtime-dir configuration is enabled.

This commit fixes that. I believe this is what caused the CI failures we
saw after 5a8ad80b6fa5 and caused it to be reverted.

[steven_wu]

LGTM. Can you use a better commit message?

[ldionne]

Rebase onto main after fixing tests

[ldionne]

Only the non-libcxx CI is failing, so I'll ship this.

libunwind/test/configs/llvm-libunwind-shared.cfg.in

 config.substitutions.append(('%{cxx}', '@CMAKE_CXX_COMPILER@'))
 config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I {}/include {}'.format('@LIBUNWIND_SOURCE_DIR@', ' '.join(compile_flags))
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nodefaultlibs -L {0}/lib -Wl,-rpath,{0}/lib -lunwind -ldl -lc {1}'.format('@CMAKE_BINARY_DIR@', ' '.join(link_flags))
+    '-nodefaultlibs -L {0} -Wl,-rpath,{0} -lunwind -ldl -lc {1}'.format('@LIBUNWIND_LIBRARY_DIR@', ' '.join(link_flags))
 ))
 config.substitutions.append(('%{exec}',
     '{} {}/utils/run.py --execdir %T -- '.format(sys.executable, '@LIBUNWIND_LIBCXX_PATH@')
 ))
 
 import os, site
 site.addsitedir(os.path.join('@LIBUNWIND_LIBCXX_PATH@', 'utils'))
 import libcxx.test.params, libcxx.test.newconfig, libcxx.test.newconfig
 libcxx.test.newconfig.configure(
     libcxx.test.params.DEFAULT_PARAMETERS,
     libcxx.test.features.DEFAULT_FEATURES,
     config,
     lit_config
 )

libunwind/test/configs/llvm-libunwind-static.cfg.in

 config.substitutions.append(('%{cxx}', '@CMAKE_CXX_COMPILER@'))
 config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
     '-nostdinc++ -I {}/include {}'.format('@LIBUNWIND_SOURCE_DIR@', ' '.join(compile_flags))
 ))
 config.substitutions.append(('%{link_flags}',
-    '-nodefaultlibs {}/lib/libunwind.a -ldl -lc {}'.format('@CMAKE_BINARY_DIR@', ' '.join(link_flags))
+    '-nodefaultlibs {}/libunwind.a -ldl -lc {}'.format('@LIBUNWIND_LIBRARY_DIR@', ' '.join(link_flags))
 ))
 config.substitutions.append(('%{exec}',
     '{} {}/utils/run.py --execdir %T -- '.format(sys.executable, '@LIBUNWIND_LIBCXX_PATH@')
 ))
 
 import os, site
 site.addsitedir(os.path.join('@LIBUNWIND_LIBCXX_PATH@', 'utils'))
 import libcxx.test.params, libcxx.test.newconfig, libcxx.test.newconfig
 libcxx.test.newconfig.configure(
     libcxx.test.params.DEFAULT_PARAMETERS,
     libcxx.test.features.DEFAULT_FEATURES,
     config,
     lit_config
 )