[scudo] Android build support

Summary:
Mark Android as supported in the cmake configuration for Scudo.

Scudo is not added yet in the Android build bots, but code builds and tests
pass locally. It is for a later CL. I also checked that Scudo builds as part
of the Android toolchain.

A few modifications had to be made:
- Android defaults to `abort_on_error=1`, which doesn't work well with the
  current tests. So change the default way to pass `SCUDO_OPTIONS` to the tests
  to account for this, setting it to 0 by default;
- Disable the `valloc.cpp` & `random_shuffle.cpp` tests on Android;
- There is a bit of gymnatic to be done with the `SCUDO_TEST_TARGET_ARCH`
  string, due to android using the `-android` suffix, and `i686` instead of
  `i386`;
- Android doesn't need `-lrt`.

Reviewers: alekseyshl, eugenis

Reviewed By: alekseyshl

Subscribers: srhines, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D37907

llvm-svn: 313538