[WebAssembly] Use hardcoded list expected undefined symbols (#21)

Rather than generate wasm.syms from wasm.js (which includes
a huge superset of the number of symbols actaully expected
to be undefined at link time) simply hardcode that list as
a test file, which lld can read.

arch/wasm32/wasm.js

@@ -951,10 +951,6 @@ var ffi = (function() {
 if (arguments.length < 1)
   throw new Error('Expected at least one wasm module to load.');
 
-if (arguments[0] == '--dump-ffi-symbols') {
-  for (var name in ffi["env"])
-    print(name)
-} else {
 function load_wasm(file_path) {
   // TODO this should be split up in load, check dependencies, and then resolve
   // dependencies. That would make it easier to do lazy loading. We could do
@@ -1035,4 +1031,3 @@ if (arguments[0] == '--dump-ffi-symbols') {
     throw e;
   }
 }
-}

arch/wasm32/wasm.syms

@@ -0,0 +1,34 @@
+# Symbols we want wasm.js to define at runtime
+_Exit
+abort
+puts
+
+# Musl syscall interface, provided by wasm.js
+__syscall
+__syscall0
+__syscall1
+__syscall2
+__syscall3
+__syscall4
+__syscall5
+__syscall6
+__syscall_cp
+
+# Symbols not supported by clang but currently expected to work on the
+# wasm waterfall
+# TODO(sbc): remove these
+__builtin_isinff
+__builtin_isinfl
+__builtin_clrsb
+__builtin_clrsbl
+__builtin_clrsbll
+__builtin_apply
+__builtin_apply_args
+__builtin_malloc
+
+# Part of musl we still don't compile for wasm
+__lock
+__unlock
+__set_thread_area
+setjmp
+longjmp