[test] Fix LLDB Python Path and re-enable linux-fatal-backtrace.swift

Author: JDevlieghere

test/lit.cfg

@@ -126,6 +126,10 @@ def get_simulator_command(run_os, run_cpu, sdk_path):
     else:
         lit_config.fatal("Unknown simulator OS %r" % run_os)
 
+def get_lldb_python_path(lldb_build_root):
+    lldb_path = os.path.join(lldb_build_root, 'bin', 'lldb')
+    return subprocess.check_output([lldb_path, "-P"]).rstrip()
+
 assert darwin_sdk_build_version_cmp("11A1", "12A1") < 0
 assert darwin_sdk_build_version_cmp("12A1", "11A1") > 0
 
@@ -1675,10 +1679,8 @@ config.substitutions.append(('%import-libdispatch', getattr(config, 'import_libd
 
 if config.lldb_build_root != "":
     config.available_features.add('lldb')
-    # Note: using the same approach to locating the lib dir as in
-    # finishSwigPythonLLDB.py in the lldb repo
-    python_lib_dir = get_python_lib(True, False, config.lldb_build_root)
-    config.substitutions.append(('%lldb-python-path', python_lib_dir))
+    lldb_python_path = get_lldb_python_path(config.lldb_build_root)
+    config.substitutions.append(('%lldb-python-path', lldb_python_path))
 
 # Disable randomized hash seeding by default. Tests need to manually opt in to
 # random seeds by unsetting the SWIFT_DETERMINISTIC_HASHING environment