WASI & darwin: support env variables based on libc

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

src/syscall/syscall_libc_wasi.go

@@ -0,0 +1,50 @@
+// +build wasi
+
+package syscall
+
+// https://github.com/WebAssembly/wasi-libc/blob/main/expected/wasm32-wasi/predefined-macros.txt
+
+type Signal int
+
+const (
+	SIGCHLD = 16
+	SIGINT  = 2
+	SIGKILL = 9
+	SIGTRAP = 5
+	SIGQUIT = 3
+	SIGTERM = 15
+)
+
+const (
+	Stdin  = 0
+	Stdout = 1
+	Stderr = 2
+)
+
+const (
+	__WASI_OFLAGS_CREAT   = 1
+	__WASI_FDFLAGS_APPEND = 1
+	__WASI_OFLAGS_EXCL    = 4
+	__WASI_OFLAGS_TRUNC   = 8
+	__WASI_FDFLAGS_SYNC   = 16
+
+	O_RDONLY = 0x04000000
+	O_WRONLY = 0x10000000
+	O_RDWR   = O_RDONLY | O_WRONLY
+
+	O_CREAT  = __WASI_OFLAGS_CREAT << 12
+	O_CREATE = O_CREAT
+	O_TRUNC  = __WASI_OFLAGS_TRUNC << 12
+	O_APPEND = __WASI_FDFLAGS_APPEND
+	O_EXCL   = __WASI_OFLAGS_EXCL << 12
+	O_SYNC   = __WASI_FDFLAGS_SYNC
+
+	O_CLOEXEC = 0
+)
+
+//go:extern errno
+var libcErrno uintptr
+
+func getErrno() error {
+	return Errno(libcErrno)
+}