Subzero, Wasm: Dynamically reallocate read buffer. Runtime improvements.

Subzero, Wasm: Dynamically reallocate read buffer. Runtime improvements.

This change fills in several more runtime functions needed by several
benchmarks, as well as changing the buffer handling in the WASM
decoder. Now the decoder will resize the buffer as needed to
accomodate large .wasm modules.

Tracing can now be enabled on runtime functions to aid with
debugging. Additionally, runtime failures such as bounds check
failures or invalid indirect function calls tell what kind of failure
occured.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4369
R=jpp@chromium.org, stichnot@chromium.org

Review URL: https://codereview.chromium.org/1918213003 .