Also, enable test misc/cgo/testcshared for android/arm64.
c/17245 and c/17246 provide the missing pieces for making
this test work.

"androidtest.bash" now passes on a Nexus 9 (volantis)
device running Android build "LMY48T".

Change-Id: Icb9fd2d17d97e0f04cb18d0cd91640c80fbd3fb4
Reviewed-on: https://go-review.googlesource.com/17333Reviewed-by: Ian Lance Taylor <iant@golang.org>