Add symbol aliasing feature to wasm-ld to support SwiftPM testing mechanism

[kateinoigakukun]

MachO and ELF linkers have features to rename symbols to another name.

e.g. for ld64

     -alias symbol_name alternate_symbol_name
                 Create an alias named alternate_symbol_name for the symbol symbol_name.  By default the alias symbol has global visibility.  This option was previous the -idef:indir option.

This feature is required in SwiftPM to link executable target with test target. Currently it's disabled for WASI because wasm-ld doesn't support it now. swiftlang/swift-package-manager#3804