ANDROID: Support disabling symbol trimming

Allow disabling symbol trimming on the command line when running
build.sh. This allows us to make GKI builds without trimming and without
modifying the build config. The main use case is when we want to update
the symbol list in a mixed build system.

Bug: 186549137
Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: I16d1c348270b4dbb378f009857286acd7b6d8aa3