Now that CMAKE_HOST_SYSTEM_NAME and CMAKE_SYSTEM_NAME are set by default to
Android in the Termux app, make the needed tweaks. Some tests were adapted
to work natively on Android too, adds sys/cdefs.h to the Bionic modulemap,
and includes the start of native Android platform support in the build-script.
The Bionic modulemap was missing the autolinking information against
libm, so using the module math functions might have hit undefined
symbols (it was happening in TestDecimal in Foundation for me). The line
is present in the Linux glibc.modulemap, but was not there for Android
Bionic modulemap.
This splits out the bionic modulemap from the glibc modulemap. They are
sufficiently different that the duplication is worth it. Furthermore,
it will enable properly identifying the libc on android. Once fully
detangled, this will enable the use of bionic on non-android platforms.
