runtime/cgo: look for android_get_device_api_level in libc.so
runtime/cgo: look for android_get_device_api_level in libc.so

The presence of the android_get_device_api_level symbol is used to
detect Android Q or later. Use the suggestion by Ryan Prichard and
look for it in libc.so and not in the entire program where someone
else might have defined it.

Manually tested on an Android Q amd64 emulator and arm64 Pixel.

Updates #29674

Change-Id: Iaef35d8f8910037b3690aa21f319e216a05a9a73
Reviewed-on: https://go-review.googlesource.com/c/go/+/170127
Run-TryBot: Elias Naur <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@eliasnaur.com>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

akutz/go,golang/go,akutz/go,josharian/go,golang/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,cloudflare/go,josharian/go,cloudflare/go,golang/go,akutz/go,CAFxX/go,akutz/go,cloudflare/go,akutz/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,josharian/go,cloudflare/go,josharian/go,golang/go,josharian/go,CAFxX/go,CAFxX/go,nawawi/go,josharian/go,josharian/go,golang/go,nawawi/go,akutz/go,golang/go,josharian/go,akutz/go,akutz/go,nawawi/go,nawawi/go