When we're compiling compiler_rt for any WebAssembly target, we do
not want to expose all the compiler-rt functions to the host runtime.
By setting the visibility of all exports to `hidden`, we allow the
linker to resolve the symbols during linktime, while not expose the
functions to the host runtime. This also means the linker can
properly garbage collect any compiler-rt function that does not get
resolved. The symbol visibility for all target remains the same as
before: `default`.
Starting with LLVM 14, the Libcalls to these functions are now lowered
using a Vec(2, u64) instead of the standard ABI for i128 integers, so
our compiler-rt implementation needs to be updated to expose the same
ABI on Windows.
The purpose of this branch is to switch to using an object file for each
independent function, in order to make linking simpler - instead of
relying on `-ffunction-sections` and `--gc-sections`, which involves the
linker doing the work of linking everything and then undoing work via
garbage collection, this will allow the linker to only include the
compilation units that are depended on in the first place.
This commit makes progress towards that goal.
