LLVM Backend generates assembly unparsable by gnu toolchains
```haskell
module Main where
import System.Random
import qualified Data.Vector as V
g1 = mkStdGen 0 :: StdGen
v2 = take 10000 $ randoms g1 :: [Int]
main :: IO ()
main = do
undefined
```
```
$ /e/ghc_regSpill/inplace/bin/ghc-stage2.exe Repro.hs -O2 -fllvm -O2
Loaded package environment from C:\ghc\msys64\home\Andi\tmp\minmax\unpred\.ghc.environment.x86_64-mingw32-8.7.20190215
[1 of 1] Compiling Main ( Repro.hs, Repro.o )
C:\\ghc\\msys64\\tmp\\ghc385768_0\\ghc_6.s: Assembler messages:
C:\\ghc\\msys64\\tmp\\ghc385768_0\\ghc_6.s:354: Error: junk at end of line, first unrecognized character is `,'
`gcc.exe' failed in phase `Assembler'. (Exit code: 1)
```
I've reproduced this with ghc 8.4/8.6 and HEAD using llvm 7.0.1 on windows.
It only occurs with -O2.
The issues arise from these directives:
```
.section .rdata,"dr",discard,__xmm@000000000000004e0000000000000000
```
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ---------------- |
| Version | 8.9 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | high |
| Resolution | Unresolved |
| Component | Compiler (LLVM) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | Unknown/Multiple |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"LLVM Backend generates invalid assembly.","status":"New","operating_system":"Unknown/Multiple","component":"Compiler (LLVM)","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"8.9","keywords":["CodeGen"],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"\r\n{{{\r\n#!haskell\r\nmodule Main where\r\n\r\nimport System.Random\r\nimport qualified Data.Vector as V\r\n\r\ng1 = mkStdGen 0 :: StdGen\r\nv2 = take 10000 $ randoms g1 :: [Int]\r\n\r\nmain :: IO ()\r\nmain = do\r\n undefined\r\n}}}\r\n\r\n\r\n{{{\r\n$ /e/ghc_regSpill/inplace/bin/ghc-stage2.exe Repro.hs -O2 -fllvm -O2\r\nLoaded package environment from C:\\ghc\\msys64\\home\\Andi\\tmp\\minmax\\unpred\\.ghc.environment.x86_64-mingw32-8.7.20190215\r\n[1 of 1] Compiling Main ( Repro.hs, Repro.o )\r\nC:\\\\ghc\\\\msys64\\\\tmp\\\\ghc385768_0\\\\ghc_6.s: Assembler messages:\r\nC:\\\\ghc\\\\msys64\\\\tmp\\\\ghc385768_0\\\\ghc_6.s:354: Error: junk at end of line, first unrecognized character is `,'\r\n`gcc.exe' failed in phase `Assembler'. (Exit code: 1)\r\n\r\n}}}\r\n\r\nI've reproduced this with ghc 8.4/8.6 and HEAD using llvm 7.0.1 on windows.\r\n\r\nIt only occurs with -O2.\r\n\r\nThe issues arise from these directives:\r\n\r\n{{{\r\n\t.section\t.rdata,\"dr\",discard,__xmm@000000000000004e0000000000000000\r\n}}}","type_of_failure":"OtherFailure","blocking":[]} -->
issue