Faced a similar issue for lldb test suites as well - "Issues running lldb-Suite test cases while building Apple Swift 5 toolchain on PowerPC64LE - #15 by stamba"
Used the 'llvm-readelf' utility to find details about the libraries linked with lldb binary and realised that the directories mentioned in RUNPATH might not have the required libraries.
Similar to reasons mentioned in my earlier issue "TestFoundation test suite failing while building Swift Toolchain - #6 by stamba", I manually copied the libraries and it worked. The lldb test suite was executed, though it fails now for only 7 test cases:-
Failing Tests (7):
LLDB :: SwiftREPL/ErrorReturn.test
LLDB :: tools/lldb-mi/symbol/symbol-list-lines.test
lldb-Suite :: lang/swift/dwarfimporter/C/TestSwiftDWARFImporterC.py
lldb-Suite :: lang/swift/reference_storage_types/TestSwiftReferenceStorageTypes.py
lldb-Suite :: lang/swift/repl_in_c/TestSwiftReplInC.py
lldb-Suite :: lang/swift/unknown_self/TestSwiftUnknownSelf.py
lldb-Suite :: lang/swift/variables/swift/TestSwiftTypes.py