build: fix cc_wrapper.py treatment of -lc++.

[htuch]

I think this was the intended code, I noticed a failure in
compile_time_options for
#5218.

Risk Level: Low
Testing: bazel build --config=libc++ //source/exe:envoy-static

Signed-off-by: Harvey Tuch htuch@google.com

[htuch]

@PiotrSikora while working on #5218, I hit this issue where compile_time_options started to fail. It pointed at a bug I think in the libc++ support.

I'd like to add a regression test for this, but I don't seem to be able to rebuild with libc++ on my gLinux workstation and clang-7. Even with the documented steps here, it complains about stdlib header issues, but then seems to work when I add debug to cc_wrapper.py. Very confused, suspect something strange with the sys.argv iteration but can't pin it down.

Can you take a look at this and let me know what your thoughts are?

[PiotrSikora]

Yes, this was definitely the intended code. Thanks for digging into this!

I guess this worked fine, because the broken code still removed -lstdc++ from the args, and -lc++ is automatically injected when using -stdlib=lc++, so it's wasn't strictly needed.