Bump base for trying more SDL2 library names (#4829)

See https://github.com/koreader/koreader/issues/4826#issuecomment-475043234

Also some Makefile/CMake sanity/cleanup/style/refactoring.

Includes:

* [build] Move Android ZLIB_LDFLAGS to thirdparty/zlib https://github.com/koreader/koreader-base/pull/870
* [chore] Update CMake to modern style with lowercase commands https://github.com/koreader/koreader-base/pull/872
* [fix] Add util.ffiLoadCandidates to try multiple SDL2 library names https://github.com/koreader/koreader-base/pull/873
* [fix] Return fail status for SDL https://github.com/koreader/koreader-base/pull/874
* [chore] Makefile: declare all phonies https://github.com/koreader/koreader-base/pull/875
* [chore] Remove luajit-clean target https://github.com/koreader/koreader-base/pull/876
* [chore] CMake kpvcrlib convert remaining tabs to four spaces https://github.com/koreader/koreader-base/pull/877

base

@@ -1 +1 @@
-Subproject commit ced414b33a50fbafcf922939703dedd92ec2bc9a
+Subproject commit a0088f5803fd05851704c792b3add0893b47b945