Check use of NGX_RPATH in auto/runtime about ngx_wasm_module

[hishamhm]

Upon a bit more investigation looks like $NGX_RPATH = YES is intended to add a -R flag with the library locations (as seen in uses such as https://github.com/nginx/nginx/blob/master/auto/lib/libgd/conf#L24-L28). Turns out the -R flag is from ld, but since we're successfully using -Wl,-rpath in our builds, I'm guessing in our case ngx_feature_libs and friends are being argument-processed by cc instead.

So I think the right patch would be to change yes to YES, and add another variable (NGX_WASM_WL_RPATH for distinction?) to control our additions of -Wl,-rpath in auto/runtime and auto/cargo, which could then be used by @flrgh to disable them in the Gateway build if needed.