put FILE in core:c and use that in bindings to fix wasm

core/c/c.odin

@@ -114,3 +114,5 @@ CHAR_BIT :: 8
 va_list :: struct #align(16) {
 	_: [4096]u8,
 }
+
+FILE :: struct {}

core/c/libc/stdio.odin

@@ -1,5 +1,6 @@
 package libc
 
+import "core:c"
 import "core:io"
 
 when ODIN_OS == .Windows {
@@ -15,7 +16,7 @@ when ODIN_OS == .Windows {
 
 // 7.21 Input/output
 
-FILE :: struct {}
+FILE :: c.FILE
 
 Whence :: enum int {
 	SET = SEEK_SET,