* 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.
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