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.
Use `clang` rather than `clang++` as the linker driver. This ensures
that we do not force a C++ runtime on the general code. This is fine
for now as C++ interop is not yet available for Swift. This prevents
the accidental mix-and-match of various C++ runtimes. This can cause
problems on platforms like android where `libstdc++` is an unsupported
runtime but is generally the default for Linux platforms.
The original support for embedded bitcode used appending linkage for the
magic internal variables that hold the bitcode and command line options,
but that private linkage is a better fit. The only real reason for
appending linkage was to prevent those variables from being optimized away.
r269706 limits the use of appending linkage so that it cannot be used for
those variables, so this switches to use private linkage and keep the
variables alive with llvm.compiler.used. This is basically copied from
clang r269679. rdar://problem/28685198.
As of the swift-3.1-branch versions of Clang/LLVM, embedded bitcode is now
working well enough that the tests can be reenabled. rdar://problem/26247134
Together with -wmo it enables multi-threaded compilation.
I didn't want to reuse the -j option for this, because -num-threads (even if n == 1) does change the generated code.
For details see commit message of r25930.
Swift SVN r26258
