Change the names of two private methods: allocate -> __vallocate and...

Change the names of two private methods: allocate -> __vallocate and deallocate -> __vdeallocate. NFC. This change triggered by https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61806, which shows up when we implement deduction guides for the container adaptors.The names have a 'v' in them because WIN32 has a macro named __deallocate. (sigh).

llvm-svn: 332996