Allow pnacl-sz to be compiled to textual bitcode records.

Allow pnacl-sz to be compiled to textual bitcode records.

This has been added to allow fuzzing to be applied to textual bitcode
records. When built with make option TEXTUAL_BITCODE=1, the
corresponding generated pnacl-sz will preprocess the input file
(containing the textual form of bitcode records) and generate
a corresponding data stream with the binary form.

Note that the texual form of bitcode records is not LLVM assembly
(i.e. .ll files). Rather, it is sequences of texual integers
corresponding to bitcode records.

Dependent on: https://codereview.chromium.org/1191393004

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4169
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1190413004