Discuss to drop -fno-integrated-as for clang

[Icenowy]

Currently llvm-as seems to be not so weird, and clang seems to have some different opinion on instructions with binutils, at least on AArch64:

• BFC, which is a pseudo instruction in ARMv8.2 (translated to a real instruction to v8.0), will be produced by clang in v8.0 mode, but rejected by GNU as in v8.0 mode.
• PMULL, which is a instruction in ARMv8.0 extension, will be produced by clang when -march=armv8-a+crc, but will only be accepted by GNU as when -march=armv8-a+aes. (of course this can be solved by +crc+aes).

[Icenowy]

Known packages to fail to build because of BFC of clang:

emscripten
yosys

[Icenowy]

kicad in testing also failed because of BFC.