Execute nacl compilers parallel if goma is available.
Execute nacl compilers parallel if goma is available.

Compilers to build NaCl-related files are invoked by build_nexe.py.
Since this sequentially execute a NaCl compiler, the leverage using goma does
not work well.

This change let build_nexe.py execute compiling parallel if it detects
goma is available.
Let me start from linux + x86-64/x86-32 + newlib/glibc.

Review URL: https://chromiumcodereview.appspot.com/15731011

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@11501 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