cmd/gomobile: fix test for buildmode=c-shared
cmd/gomobile: fix test for buildmode=c-shared

Added recently, but I forgot to update the test.

Fixes golang/go#12983

Change-Id: I668b20d74c6b91d9588e6f252939d36ae780bd77
Reviewed-on: https://go-review.googlesource.com/16052
Reviewed-by: Hyang-Ah Hana Kim <d7e82c3c07f92613bcbf9a1e88f6b96c13caa3b0@gmail.com>

golang/mobile,golang/mobile,golang/mobile,golang/mobile