Bug#975692: assembler fix required for gcn offload compiler

[Matthias Klose]

Control: reopen -1

apparently that's not good enough, at least for the LLVM 11 branch.

https://buildd.debian.org/status/fetch.php?pkg=gcc-10&arch=amd64&ver=10.2.1-2&stamp=1608664737&raw=0

[...]
/tmp/ccQFzQVM.s:1082:2: error: changed section flags for .rodata.cst8, expected:
0x12
        .section        .rodata.cst8
        ^
/tmp/ccQFzQVM.s:1082:2: error: changed section entsize for .rodata.cst8, expected: 8
        .section        .rodata.cst8
        ^
make[10]: *** [Makefile:980: lib_a-wcstod.o] Error 1

reverting to LLVM 9 for now.