Fix the "opt-win" build on Visual Studio 10.0
Fix the "opt-win" build on Visual Studio 10.0

Before the change, linking fails with:
LINK : fatal error LNK1117: syntax error in option 'PDBPATH:none'

"/PDBALTPATH:%_PDB%" works on both MSVC 9.0 and 10.0 and has the same
effect of omitting the absolute pathname from the executable.

Both before and after, we get:
$ strings scons-out/opt-win-x86-32/staging/ncdecode_table.exe | grep -i pdb
ncdecode_table.pdb

BUG=http://code.google.com/p/nativeclient/issues/detail?id=1287
TEST=build with Windows SDK + trybots

Review URL: http://codereview.chromium.org/6031015

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@4077 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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