Fix fallout from the merge.

- CI merge issues:
   - The malloc shim libraries are renamed.
   - CMake gets very unhappy if you don't enable the C language and
     tries to link with the C compiler instead of the C++ compiler if
     you do enable it.
   - The Ubuntu packages for QEMU install a `binfmt_misc` activator for
     PowerPC64 little-endian, but set the page size to 4 KiB.  We then
     tried to run the tests (which expect 64 KiB pages) and became very
     confused when `mmap` returned 4 KiB-aligned memory.
 - Test failures:
   - Fix all of the issues UBsan found.
     - Underflow in `pointer_offset` when used to add negative offsets.
     - `CoreAlloc`'s `LocalState` accessed on a null `CoreAlloc` pointer.
     - Out of bounds access in the sizeclass list on attempts to access
       more memory than fits in the VA space.
     -
   - There was an integer overflow in `AddressSpace` that could cause it
     to try to allocate a zero-sized object, get a null pointer, and
     then try to do something with 0 - {size of the real allocation}.
   - The malloc tests weren't setting `errno` to 0 before doing
     calling `malloc`, which should set `errno` on failure, and then
     checking that `errno` was 0.
   - Don't call `PAL::error` on PAL allocation failure, return `nullptr`.
     The PALs were inconsistent about that and the new code expects to be
     able to report address-space exhaustion.
   - The malloc checks can behave differently with 0-sized allocations
     on different platforms but were very fragile about their
     expectations.
   - The malloc test didn't report failure for all of the ways that it
     could fail and so was spuriously passing on some platforms.
   - The perf test for external pointer is currently very slow on
     Windows.  The number of loops have been reduced and a timeout added
     for the Windows CI runs.
   - The logic to capture `errno` across calls was using
     `decltype(errno)`, which on some platforms where `errno` is a macro
     evaluated to `int&` and so they captured a reference rather than
     the value and failed to reset `errno`.
   - The Apple PAL can set `errno` on `notify_using` if it's called with
     memory that was not previously passed to `notify_not_using` but was
     not adequately protected against this and so would sometimes cause
     `malloc` to set `errno` to `EINVAL`.

src/test/perf/external_pointer/externalpointer.cc

@@ -53,7 +53,9 @@ namespace test
   void test_external_pointer(xoroshiro::p128r64& r)
   {
     auto& alloc = ThreadAlloc::get();
-#ifdef NDEBUG
+    // This is very slow on Windows at the moment.  Until this is fixed, help
+    // CI terminate.
+#if defined(NDEBUG) && !defined(_MSC_VER)
     static constexpr size_t iterations = 10000000;
 #else
 #  ifdef _MSC_VER