Bug#930008: clang-8: --target=arm-linux-gnueabihf should target armv7 instead of armv6

[Mike Hommey]

Package: clang-8
Version: 1:8-3
Severity: wishlist

Dear Maintainer,

The target that one gives to clang needs, to some extent, to match what
the toolchain prefix is for binutils. For armhf, that is
arm-linux-gnueabihf. When using clang --target=arm-linux-gnueabihf,
clang still targets armv6, when the baseline for the armhf Debian
architecture is armv7. It should arguably target armv7.

```
$ clang --target=arm-linux-gnueabihf -dM -E -xc - < /dev/null | grep ARM_ARCH
#define __ARM_ARCH 6
#define __ARM_ARCH_6KZ__ 1
#define __ARM_ARCH_ISA_ARM 1
#define __ARM_ARCH_ISA_THUMB 1
```

One can use --target=armv7-linux-gnueabihf, but then clang doesn't find
the arm-linux-gnueabihf-prefixed binutils tools.

Mike