Require that the module symbol table can't appear after function.

The bitcode parser assumes that the module symbol table, if it exists,
must appear before the first function
block (i.e. defininition). However, the parser did not check this
constraint. This patch fixes that omission.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4320
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1359923002 .
3 files changed