C API: dylib on macOS has ID with rpath

[turbolent]

Describe the bug

Similar to bytecodealliance/wasmtime#984:

On macOS, the built dylib has an ID with a relative path, @rpath:

$ otool -L wasmi/lib/libwasmi.dylib
wasmi/lib/libwasmi.dylib:
	@rpath/libwasmi.dylib (compatibility version 0.0.0, current version 0.0.0)
	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1351.0.0

Loading the dynamic library then results in

Library not loaded: @rpath/libwasmi.dylib

Reason: no LC_RPATH's found

Expected behavior

Loading the built dynamic library should work.

To Reproduce

1. What Wasmi version was used?

68205d4

2. Bug occurs on Wasmi CLI or Wasmi library?

Wasmi C library

3. Ideally please provide minified Wasm (.wasm) or Wat (.wat) file to reproduce.

N/A

4. Follow steps in https://lib.rs/crates/wasmi_c_api_impl

5. Link against the dylib and run the binary

[turbolent]

I've solved this for now by post-processing the library manually with e.g.

$ install_name_tool -id libwasmi.dylib libwasmi.dylib

wasmtime has a build step to do this automatically, this could be maybe adopted here:
https://github.com/bytecodealliance/wasmtime/blob/06377eb08a649619cc8ac9a934cb3f119017f3ef/crates/c-api/CMakeLists.txt#L108-L114

[Robbepop]

@turbolent Thanks a lot for the issue report! Since you already know what needs to be done (e.g. Wasmtime's solution), would you be willing to open a PR? :)

[turbolent]

It looks like wasmi's CMake configuration already has code for this:

wasmi/crates/c_api/CMakeLists.txt

Lines 115 to 133 in 7a302a9

	if(WASMI_TARGET MATCHES "darwin")
	set(INSTALLED_LIB "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}/libwasmi.dylib")
	install(
	FILES "${INSTALLED_LIB}"
	DESTINATION "${CMAKE_INSTALL_PREFIX}/${CMAKE_INSTALL_LIBDIR}"
	COMPONENT Runtime
	)
	if(NOT CMAKE_INSTALL_NAME_TOOL)
	message(WARNING "CMAKE_INSTALL_NAME_TOOL is not set. LC_ID_DYLIB for libwasmi.dylib will not be set.")
	else()
	set(install_name_tool_cmd
	"${CMAKE_INSTALL_NAME_TOOL}"
	"-id"
	"@rpath/libwasmi.dylib"
	"${INSTALLED_LIB}"
	)
	install(CODE "execute_process(COMMAND ${install_name_tool_cmd})")
	endif()
	endif()

I'm not familiar enough with the macOS linker to say what the behaviour should be.