[asan] Make __cxa_demangle non-weak symbol on Android.

This fixes global-demangle.cc test on Android.

https://code.google.com/p/address-sanitizer/issues/detail?id=264


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@201545 91177308-0d34-0410-b5e6-96231b3b80d8