don't pass --fix-cortex-a8 with lld

[DanAlbert]

Not yet supported: #766

We should avoid passing that when the user is using lld.

[DanAlbert]

(I'm considering doing this for r18, but since beta 2 is already out I'm hesitant to make a non-regression-fix change)

[arturbac]

There is connected issue when somone uses full llvm compiler,assembler,linker
android cmake toolchain adds -fno-integrated-as and -Wa,--noexecstack
Whith ndk 18 i can use full llvm with lto-thin but i have to:

• add -fintegrated-as (override at the end of compile options or replace -fno-integrated-as)
• remove -Wa,--noexecstack
  Then everyting is build with llvm without binutils. and thin lto works, but i didnt check how it works with binutils as and lld, maybe it works too.
  I think android cmake toolchain could support using full llvm (as,lld too) as an option