Build as PIE in Gyp build.
Build as PIE in Gyp build.

We've been building executables as PIEs for a while under SCons.
But the Gyp rules were never updated to match.

Note that there are still various other details of flag settings where Gyp
doesn't match SCons.  Since nobody actually uses the Gyp-built binaries of
standalone NaCl stuff, these have gone unnoticed and untested.  All the
compilation and linking flags should be updated in Gyp to match Scons at
some point.

BUG= http://code.google.com/p/nativeclient/issues/detail?id=2622
TEST= trybots

R=bsy@google.com

Review URL: https://chromiumcodereview.appspot.com/9537018

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@7913 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client