Scaffold in OCIO compatibility for Android

This commit makes the following changes to our Android build:

- Removal of the ECM hack for DSO linking. This is incompatible with
static libraries on x86 because of "relocation R_386_GOTOFF against
preemptible symbol". I've made a local build without issues.
- Use a consistent Android STL across Krita and its dependencies. This
prevents the infamous abort on unwind when handling OCIO exceptions [1].
- Patch OCIO so that Android toolchain specs are propagated to its static
dependencies. This fixes linking issues on x86, because the static
libraries were built for armv7a by default. This patch will be
upstreamed separately.

Please notice that OCIO is still *not* shipped with Krita, because it
is unable to read configuration files natively due to the Scoped
Storage "feature" of Android [2]. A prospective dev or tester
can uncomment the ext_ocio line on androidbuild.sh.

[1]: https://github.com/android/ndk/issues/1441
[2]: https://developer.android.com/about/versions/11/privacy/storage#scoped-storage

CCMAIL: kimageshop@kde.org