Allow alternate name for NaCl entry point.
Allow alternate name for NaCl entry point.

This change allows the newlib _start function to use
'__nacl_main' as the entry point in place of 'main'.
The normal 'main' entry point is still used if no
'__nacl_main' symbol is linked into the binary.

BUG= http://code.google.com/p/chromium/issues/detail?id=246246
R=mcgrathr@chromium.org

Review URL: https://codereview.chromium.org/16057006

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@11747 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

Lind-Project/native_client,Lind-Project/native_client,Lind-Project/native_client,Lind-Project/native_client,Lind-Project/native_client,Lind-Project/native_client