Clean up the obsolete asan=1 config bits:

Clean up the obsolete asan=1 config bits:
 -- 10.5 isn't supported anymore, so we don't need to pass -Wl,-U for undefined symbols
 -- third_party/llvm-build is now used for ASan, so the Chromium clang plugins should be fully supported.

TBR=thakis 
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=154128

[Alexander Potapenko, 2012-08-30 11:17:11]

TBR

[Nico, 2012-08-30 15:42:05]

lgtm