Wasm: add __syscall implementation for the sake of __syscall_cp

Author: NWilson

src/internal/wasm/syscall.c

@@ -0,0 +1,25 @@
+#include <stdarg.h>
+#include "syscall.h"
+
+/* This is hardly required at all... in all but one place in the
+ * Musl codebase, the __syscall macro is able to redirect to
+ * __syscallN directly, but in __syscall_cp there's an exception
+ * where the varargs version is called explicitly.  We therefore
+ * need this extra stub.
+ *
+ * TODO See if we can get __syscall_cp to be changed, or move this
+ * stub into src/internal/syscall.c so it's not necessary to do
+ * this in the Wasm arch code.
+ */
+long (__syscall)(long n, ...)
+{
+	va_list va;
+	va_start(va, n);
+	long a1 = va_arg(va, long);
+	long a2 = va_arg(va, long);
+	long a3 = va_arg(va, long);
+	long a4 = va_arg(va, long);
+	long a5 = va_arg(va, long);
+	long a6 = va_arg(va, long);
+	return __syscall6(n, a1, a2, a3, a4, a5, a6);
+}