Fixes: #1549

A bunch of `#ifdef` stuff cleanups, including:

- Check header presence with `__has_include` instead of autoconf's
`HAVE_XXX` macro
- Standartization of defines: consistent naming, define to 1 and check
with `#if` instead of `#ifdef`
- Compile MBROLA-related code only if configured `--with-mbrola`
- Compile tests with flags that match configuration (including async,
klatt, speechplayer, mbrola)
- Fix for API test when compiled with async

ref: #1554
ref for buffer size:
a6fb239208/source/synthDrivers/_espeak.py (L338)

ref: #1554
ref for buffer size: a6fb239208/source/synthDrivers/_espeak.py (L338)

Ref: #1549

Contribute to #68 

Reduce number of externs and static-returns

- Add more compilers - especially GCC on macOS and Clang.
- Add more architectures - especially RISC-V-64
- Move build outside of QEMU (use cross-compilation)
- Use qemu-user for test on target environment
- Add Android CI with APK artifacts

Found with pmd-cpd scanner. The new function could probably be named better.

Contribute to #68

Tidying up a data source bundle, that is embedded e.g. in iOS app

Contribute to #68

Reduce count of globals / externs that could be a file-local static
variables