* build-exe does include the startup code that supplies _start for the
wasm32-freestanding target. Previously this did not occur because
of logic excluding "freestanding".
* build-lib for wasm32-freestanding target gets linked by LLD. To avoid
infinite recursion, compiler_rt and zig libc are built as objects
rather than libraries.
- no "lib" prefix and ".wasm" extension instead of ".a". Rather than
build-lib foo.zig producing "libfoo.a", now it produces "foo.wasm".
* go back to using `.o` extension for webassembly objects
* zig libc only provides _start symbol for wasm when linking libc.
* rename std/special/builtin.zig to std/special/c.zig
not to be confused with @import("builtin") which is entirely
different, this is zig's multi-target libc implementation.
* WebAssembly: build-exe is for executables which have a main().
build-lib is for building libraries of functions to use from,
for example, a web browser environment.
- for now pass --export-all for libraries when there are any
C objects because we have no way to detect the list of exports
when compiling C code.
- stop passing --no-entry for executables. if you want --no-entry
then use build-lib.
* make the "musl" ABI the default ABI for wasm32-freestanding.
* zig provides libc for wasm32-freestanding-musl.
