[analyzer] Tests: move system functions into system header simulator files.

Some checkers ascribe different behavior to functions declared in system
headers, so when working with standard library functions it's probably best
to always have them in a standard location.

Test change only (no functionality change), but necessary for the next commit.
[analyzer] Properly invalidate global regions on opaque function calls.

This fixes a regression where a call to a function we can't reason about
would not actually invalidate global regions that had explicit bindings.

  void test_that_now_works() {
    globalInt = 42;
    clang_analyzer_eval(globalInt == 42); // expected-warning{{TRUE}}

    invalidateGlobals();
    clang_analyzer_eval(globalInt == 42); // expected-warning{{UNKNOWN}}
  }

This has probably been around since the initial "cluster" refactoring of
RegionStore, if not longer.

<rdar://problem/13464044>
[analyzer] Re-enable using global regions as a symbolic base.

Now that we're invalidating global regions properly, we want to continue
taking advantage of a particular optimization: if all global regions are
invalidated together, we can represent the bindings of each region with
a "derived region value" symbol. Essentially, this lazily links each
global region with a single symbol created at invalidation time, rather
than binding each region with a new symbolic value.

We used to do this, but haven't been for a while; the previous commit
re-enabled this code path, and this handles the fallout.

<rdar://problem/13464044>
[analyzer] Be lazy about struct/array global invalidation too.

Structs and arrays can take advantage of the single top-level global
symbol optimization (described in the previous commit) just as well
as scalars.

No intended behavioral change.
Numeric parsing was getting the wrong answer when faced with very long inputs.  This fixes both http://llvm.org/bugs/show_bug.cgi?id=15751 and http://llvm.org/bugs/show_bug.cgi?id=15740