cmd/cgo: use --no-gc-sections if available

cmd/cgo: use --no-gc-sections if available

zig cc passes `--gc-sections` to the underlying linker, which then
causes undefined symbol errors when compiling with cgo but without C
code. Add `-Wl,--no-gc-sections` to make it work with zig cc. Minimal
example:

**main.go**

    package main
    import _ "runtime/cgo"
    func main() {}

Run (works after the patch, doesn't work before):

    CC="zig cc" go build main.go

Among the existing code, `src/runtime/testdata/testprognet` fails to
build:

    src/runtime/testdata/testprognet$ CC="zig cc" go build .
    net(.text): relocation target __errno_location not defined
    net(.text): relocation target getaddrinfo not defined
    net(.text): relocation target freeaddrinfo not defined
    net(.text): relocation target gai_strerror not defined
    runtime/cgo(.text): relocation target stderr not defined
    runtime/cgo(.text): relocation target fwrite not defined
    runtime/cgo(.text): relocation target vfprintf not defined
    runtime/cgo(.text): relocation target fputc not defined
    runtime/cgo(.text): relocation target abort not defined
    runtime/cgo(.text): relocation target pthread_create not defined
    runtime/cgo(.text): relocation target nanosleep not defined
    runtime/cgo(.text): relocation target pthread_detach not defined
    runtime/cgo(.text): relocation target stderr not defined
    runtime/cgo(.text): relocation target strerror not defined
    runtime/cgo(.text): relocation target fprintf not defined
    runtime/cgo(.text): relocation target abort not defined
    runtime/cgo(.text): relocation target pthread_mutex_lock not defined
    runtime/cgo(.text): relocation target pthread_cond_wait not defined
    runtime/cgo(.text): relocation target pthread_mutex_unlock not defined
    runtime/cgo(.text): relocation target pthread_cond_broadcast not defined
    runtime/cgo(.text): relocation target malloc not defined

With the patch both examples build as expected.

@ianlancetaylor suggested:

> It would be fine with me if somebody wants to send a cgo patch that
passes -Wl,--no-gc-sections, with a fallback if that option is not
supported.

... and this is what we are doing. Tested with zig
0.10.0-dev.2252+a4369918b

Fixes #52690

Change-Id: Ib6d1b2bd59335e9663afefd360ddad7da358a938
GitHub-Last-Rev: 58406b36cabec694003b2c50533220410853e295
GitHub-Pull-Request: golang/go#52815
Reviewed-on: https://go-review.googlesource.com/c/go/+/405414
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>