GHC driver inadequately reverses C/C++ compiler flag order from settings file

Context: I tried to add -Xclang -target-abi -Xclang experimental-mv to CONF_CC_OPTS_STAGE2 when doing a GHC build targeting wasm32, and these flags do end up correctly in the settings file, and the GHC driver is supposed to pass them to clang. However, rts would fail to configure with: clang: error: no such file or directory: 'experimental-mv'. So I took a look at the process creation logs and discovered that, wasm32-wasi-ghc would actually pass "experimental-mv","-Xclang","-target-abi","-Xclang" to clang!

The culprit seems to be https://gitlab.haskell.org/ghc/ghc/-/blob/master/compiler/GHC/SysTools/Tasks.hs?ref_type=heads#L178. getOpts would actually reverse opt_c, which contains a mixture of C compiler flags parsed from settings and also from -optc. So the whole thing works when the C compiler flags in settings happen to be commutative, but this assumption does not always hold.

This looks like a bug worth fixing for me. The C/C++ compiler flag order from settings should be preserved, a simple reversal is a bad way to ensure user supplied -optc flags override the default flags.