Bug 1325632 - part 5 - ensure that we compile with -fno-sized-deallocation when possible; r=chmanchester

We currently turn off the C++14 sized-deallocation facility on MSVC, and
we'd like to ensure we do the same thing for clang and gcc.  To do so,
we add new functionality to moz.configure for checking and adding
compilation flags, similar to the facility for checking and adding
warning flags.  The newly added facility is then used to add
-fno-sized-deallocation to the compilation flags, when the option is
supported.

Once we do this, we can't define the sized deallocation functions in
mozalloc.h; the compiler will complain that we are using
-fno-sized-deallocation, yet defining these special functions that we'll
never use.  These functions were added for MinGW, where we needed to
compile with C++14 ahead of other platforms to be compatible with MSVC
headers.  But they're no longer necessary, though they would be if we
removed -fno-sized-deallocation; the compiler will complain if we do
that and we'll add them back at that point.