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

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 5a8ad80 and caused it to be reverted.

Differential Revision: https://reviews.llvm.org/D112322

Author: ldionne

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

@@ -47,7 +47,7 @@ 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@')

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

@@ -49,7 +49,7 @@ 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@')