ANDROID: enable LLVM_IAS=1 for clang's integrated assembler for x86_64

Step 8 of:
https://android.googlesource.com/platform/prebuilts/clang/host/linux-x86/+/master/BINUTILS_KERNEL_DEPRECATION.md



Bug: 141693040
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Change-Id: I9d1621f6484c0402a7518ffb12a3f8f3815f43a9