cc-wrapper: Use case statements instead of bunch of if/elif checks
cc-wrapper: Use case statements instead of bunch of if/elif checks

Makes for easier to read code imo, case-in-point there was a duplicate test for
`$p = -E` before. While doing this little bit of refactor I changed rest ->
kept because that makes more sense, rest sounds like its the rest of params
while kept says these are the params that we've kept.

I tested for no change in behavior using the following bash script:

```
reset() {
	cInclude=1
	cxxInclude=1
	cxxLibrary=1
	dontLink=0
	isCxx=0
	nonFlagArgs=0
	params=()
}

parseParams() {
	declare -i n=0
	nParams=${#params[@]}
	while (("$n" < "$nParams")); do
		p=${params[n]}
		p2=${params[n + 1]:-} # handle `p` being last one

		case "$p" in
		-[cSEM] | -MM) dontLink=1 ;;
		-cc1) cc1=1 ;;
		-nostdinc) cInclude=0 cxxInclude=0 ;;
		-nostdinc++) cxxInclude=0 ;;
		-nostdlib) cxxLibrary=0 ;;
		-x)
			case "$p2" in
			*-header) dontLink=1 ;;
			c++*) isCxx=1 ;;
			esac
			;;
		-?*) ;;
		*) nonFlagArgs=1 ;; # Includes a solitary dash (`-`) which signifies standard input; it is not a flag
		esac
		n+=1
	done
}

for p in c S E M MM; do
	reset
	params=-$p
	parseParams
	[[ $dontLink != 1 ]] && echo "expected dontLink=1 for params:${params[@]}" >&2 && exit 1
done

reset
params=(-x foo-header)
parseParams
[[ $dontLink != 1 ]] && echo "expected dontLink=1 for params:${params[@]}" >&2 && exit 1

reset
params=(-x c++-foo)
parseParams
[[ $isCxx != 1 ]] && echo "expected isCxx=1 for params:${params[@]}" >&2 && exit 1

reset
params=-nostdlib
parseParams
[[ $cxxLibrary != 0 ]] && echo "expected cxxLibrary=0 for params:${params[@]}" >&2 && exit 1

reset
params=-nostdinc
parseParams
[[ $cInclude != 0 ]] && echo "expected cInclude=0 for params:${params[@]}" >&2 && exit 1
[[ $cxxInclude != 0 ]] && echo "expected cxxInclude=0 for params:${params[@]}" >&2 && exit 1

reset
params=-nostdinc++
parseParams
[[ $cxxInclude != 0 ]] && echo "expected cxxInclude=0 for params:${params[@]}" >&2 && exit 1

reset
params=-cc1
parseParams
[[ $cc1 != 1 ]] && echo "expected cc1=1 for params:${params[@]}" >&2 && exit 1

reset
params=-
parseParams
[[ $nonFlagArgs != 1 ]] && echo "expected nonFlagArgs=1 for params:${params[@]}" >&2 && exit 1

reset
params=bleh
parseParams
[[ $nonFlagArgs != 1 ]] && echo "expected nonFlagArgs=1 for params:${params[@]}" >&2 && exit 1

reset
params=-?
parseParams
[[ $nonFlagArgs != 0 ]] && echo "expected nonFlagArgs=0 for params:${params[@]}" >&2 && exit 1

exit 0
```

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