gcc-8 produces "attribute directive ignored" warning for
no_sanitize("unsigned-integer-overflow"); at some point gcc will
introduce integer sanitizer support and we'll have to do this all over
again but for now just don't emit the attribute.

Mention ubsan fixes; these fixes probably fix compact mode on some
64-bit architecture where unaligned pointer reads aren't valid as well
but it's probably not very relevant...

Several tests got the buffer size wrong when sizeof(char_t)>1, and one
test didn't meet the carefully tuned allocation criteria under compact
mode due to the hash table usage and had to be changed a bit.

We were using << compact_alignment_log2 instead of * compact_alignment
for symmetry with the encoding where >> is crucial to keep code fast and
round to negative infinity.

For decoding, the results are the same and any reasonable compiler
should convert *4 into <<2 so just use a multiplication - that doesn't
trigger UB on negative numbers.

We were using allocate_memory to allocate struct xml_extra_buffer that
contains pointers; with compact mode, this allocation can be misaligned
by 4b with 8b pointers; fix this by manually realigning the pointer.

We were misaligning document data on 64-bit platforms by placing 8b
pointers at 4b offsets; fix this by reserving a full pointer worth of
bytes for page marker.

Define noexcept using _MSC_VER instead of _MSC_FULL_VER (first release
of MSVC 2015 should have it), remove redundant PUGIXML_HAS_NOEXCEPT and
define PUGIXML_NOEXCEPT_IF_NOT_COMPACT in terms of PUGIXML_NOEXCEPT.

Still trying to decide if the next version should be 1.9 or 1.8x and
what other changes need to go in.

* Adds noexcept specifiers to the move special members of xml_document, but only #ifndef PUGIXML_COMPACT

* Adds a macro definition to be able to use noexcept with supporting compilers

* Adds noexcept specifier to move special members of xpath_node_set, xpath_variable_set and xpath_query, but not of xml_document as it has a throwing implementation

Enables usage of override specifier for MSVC compilers

Enables usage of override specifier for MSVC compilers (beginning with 17.0 which is the compiler of Visual Studio 2012)

Texas Instruments compiler produces this warning for unused template
member functions:

	"pugixml.cpp", line 253: warning #179-D: function
	"pugi::impl::<unnamed>::auto_deleter<T>::release [with
	T=pugi::impl::<unnamed>::xml_stream_chunk<char>]" was declared but
	never referenced

As far as I can tell, this is a compiler issue - these functions should
not be instantiated in the first place; while it's possible to rework
the code to work around this, the changes would be fragile. It seems
best to just disable this warning - we've seen something similar on SNC
(which appears to use the same frontend!..).

Fixes #182.

It looks like there are several cases where this might happen:

- In some MinGW distributions, the LLONG_MIN/etc defines are guarded
with:

	#if !defined(__STRICT_ANSI__) && defined(__GNUC__)

Which means that you don't get them in strict ANSI mode. The previous
workaround was specifically targeted towards this.

- In some GCC distributions (notably GCC 6.3.0 in some configurations),
LLONG_MIN/etc. defines are guarded with:

	#if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 199901L)

But __STDC_VERSION__ isn't defined as C99 even if you use -std=c++14 -
which is probably technically valid, but not useful.

To work around this, redefine the symbols whenever we are building with
GCC and we need them and they aren't defined - doing this is better than
not building. Instead of hard-coding the constants, use GCC-specific
__LONG_LONG_MAX__ to compute them.

Fixes #181.

Cmake touchups

<mesh> node attribute name is "name", not "mesh".

tests: Fix OSX test failure

Apparently at some point OSX behavior when reading /dev/tty switched
from "can't open the file" to "the file can be opened and 0 bytes can be
read from it" which generates a wrong error and doesn't exercise the
code path we care about.

Fixes #176.

This makes it a bit faster and matches other internal code better.

The static_buffer optimization seems to come from the time where the
on-heap buffer was allocated using global memory operations. At this
point the temporary buffer and temporary string storage all come from
the evaluation stack (that can be partially allocated on heap...), so
the extra logic isn't relevant for performance.

This change implements move ctor and assign support for xml_document.

All node handles remain valid after the move and point to the new document; the only exception is the document node itself (that remains unmoved).

Move is O(document size) in theory because it needs to relocate immediate document children (there is just one in conformant documents) and all memory pages; in practice the memory pages only need the header adjusted, which is ~0.1% of the actual data size.

Move requires no allocations in general, except when using compact mode where some moves need to grow the hash table which can fail (throw).

Fixes #104

This helps make sure our error handling logic works and is exercised.

In compact mode, we currently can not support zero-allocation moves
since some pointer assignments required during the move need to allocate
hash table slots.

This is mostly applicable to xml_document_struct::first_child, since the
pointer to this element is used as a hash table key, but there are some
contrived cases where parents of root's children need a hash slot and
didn't have it before.

These cases can be fixed by changing the compact encoding to be a bit
more move friendly, but for now it's easier to handle the error and
throw/return during move.

When this happens, the source document doesn't change.

This allows us to do a single reserve for a known amount of assignments
that is larger than the default minimum per reserve (16).

This makes sure that MSVC shared library build actually exports all the
needed symbols and generates import table.

Somehow, this is actually enough to make pugixml link as a DLL - there's
no need to specify __declspec(dllimport) even though pugixml exports
classes via DLL.

Fixes #113.

This warning is new as of GCC 7 and highlights undefined behavior in the
preprocessor that ASAN detection was relying on.

These days OSX clang supports UB sanitizer so we can just use the same
settings for all systems.

The old fuzzer location is deprecated; this also makes it almost trivial
to fuzz, provided that the clang is set up correctly... on Ubuntu 17.10,
a command sequence like this works now:

    sudo apt install clang-5.0
    sudo apt install libfuzzer-5.0
    sudo cp /usr/lib/llvm-5.0/lib/libFuzzer.a /usr/lib/libLLVMFuzzer.a
    CXX=clang++-5.0 make fuzz_parse