Use lld as linker

[lizan]

As a part of tool chain revisit (#4159, #4158) and also as a part of (#3741). We should consider use LLD as default linker. LLD is at least twice faster than gold linker, we have more than 300 test target to link so this will improve CI performance.

Options:

1. Use lld everywhere (it works with gcc)
2. Use lld where clang is used (sanitizers)

A sample benchmark of linking envoy-static is here:

gold w/o threads (current):
12.01s user 1.32s system 99% cpu 13.358 total

gold w/ threads:
14.24s user 6.97s system 180% cpu 11.762 total

lld w/o threads:
3.63s user 1.15s system 99% cpu 4.805 total

lld w/ threads:
8.64s user 11.24s system 709% cpu 2.802 total

[mattklein123]

@lizan +1 I think we should switch to lld everywhere, especially if we switch the release build over to clang.

[mattklein123]

This is done.

[lizan]

@mattklein123 This is done for 2., I would like to still keep this open for 1.?

[mattklein123]

Ah ok. SGTM.

[htuch]

@lizan what if we do this; we point tools/bazel.rc at a shell script that detects if lld is present and uses that by default, otherwise falls backs to ld?