Use std::replace for replacing chars in strings.

Find uses of `cmSystemTools::ReplaceString` where both `replace` and
`with` are string literals with a size of one.

Automate with:

git grep -l ReplaceString | xargs sed -i "s|cmSystemTools::ReplaceString(\([^,]*\), \"\(.\)\", \"\(.\)\");|std::replace(\1.begin(), \1.end(), '\2', '\3');|g"
git grep -l ReplaceString | xargs sed -i "s|cmSystemTools::ReplaceString(\([^,]*\), \"\(.\)\", \"\\\\\\\\\");|std::replace(\1.begin(), \1.end(), '\2', '\\\\\\\\');|g"
git grep -l ReplaceString | xargs sed -i "s|cmSystemTools::ReplaceString(\([^,]*\), \"\\\\\\\\\", \"\(.\)\");|std::replace(\1.begin(), \1.end(), '\\\\\\\\', '\2');|g"