We recently noticed that the unwrap_iter.h file was pushing macros,
but it was pushing them again instead of popping them at the end of
the file. This led to libc++ basically swallowing any custom definition
of these macros in user code:

    #define min HELLO
    #include <algorithm>
    // min is not HELLO anymore, it's not defined

While investigating this issue, I noticed that our push/pop pragmas
were actually entirely wrong too. Indeed, instead of pushing macros
like `move`, we'd push `move(int, int)` in the pragma, which is not
a valid macro name. As a result, we would not actually push macros
like `move` -- instead we'd simply undefine them. This led to the
following code not working:

    #define move HELLO
    #include <algorithm>
    // move is not HELLO anymore

Fixing the pragma push/pop incantations led to a cascade of issues
because we use identifiers like `move` in a large number of places,
and all of these headers would now need to do the push/pop dance.

This patch fixes all these issues. First, it adds a check that we
don't swallow important names like min, max, move or refresh as
explained above. This is done by augmenting the existing
system_reserved_names.gen.py test to also check that the macros
are what we expect after including each header.

Second, it fixes the push/pop pragmas to work properly and adds
missing pragmas to all the files I could detect a failure in via
the newly added test.

rdar://121365472