[BE] Do not assign string literal to `char *` (#87949)
Not sure, what I was thinking when writing something like:
```
auto foo = std::getenv("BAR");
if (!foo) {
foo = "baz";
}
```
as `std::getenv` return `char *` (i.e. mutable string), but string literals are immutable. (i.e. `const char *`)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87949
Approved by: https://github.com/kit1980
