EnvironGetenv: use strncmp instead of strlen and memcmp (#27632)
EnvironGetenv: use strncmp instead of strlen and memcmp (#27632)

Instead of iterating twice over the string, first for searching the
null-terminator and then to compare it to `name`, we only iterate
over it once.
poizan42/coreclr,cshung/coreclr,cshung/coreclr,cshung/coreclr,poizan42/coreclr,cshung/coreclr,poizan42/coreclr,cshung/coreclr,poizan42/coreclr,poizan42/coreclr,cshung/coreclr,poizan42/coreclr