fsapi: adds Oflag to decouple from syscall package (#1586)

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/sysfs/open_file_linux.go

@@ -0,0 +1,28 @@
+package sysfs
+
+import (
+	"syscall"
+
+	"github.com/tetratelabs/wazero/internal/fsapi"
+)
+
+const supportedSyscallOflag = fsapi.O_DIRECTORY | fsapi.O_DSYNC | fsapi.O_NOFOLLOW | fsapi.O_NONBLOCK | fsapi.O_RSYNC
+
+func withSyscallOflag(oflag fsapi.Oflag, flag int) int {
+	if oflag&fsapi.O_DIRECTORY != 0 {
+		flag |= syscall.O_DIRECTORY
+	}
+	if oflag&fsapi.O_DSYNC != 0 {
+		flag |= syscall.O_DSYNC
+	}
+	if oflag&fsapi.O_NOFOLLOW != 0 {
+		flag |= syscall.O_NOFOLLOW
+	}
+	if oflag&fsapi.O_NONBLOCK != 0 {
+		flag |= syscall.O_NONBLOCK
+	}
+	if oflag&fsapi.O_RSYNC != 0 {
+		flag |= syscall.O_RSYNC
+	}
+	return flag
+}