This patch adds a copy of vswhere.exe to build/win32, downloaded from the
current latest release (1.0.62):
https://github.com/Microsoft/vswhere/releases/download/1.0.62/vswhere.exe
It changes toolchain.configure to invoke vswhere.exe instead of reading
the registry, since that no longer works for VS2017 (but vswhere can locate
VS2015). It also removes a layer of complexity in that code by dropping
support for non-64-bit host systems, since we don't really support building
on 32-bit Windows anymore anyway.
There's a little bit of fixup in windows.configure where some LIB paths
have changed in 2017.
MozReview-Commit-ID: 5XLWjidS6W4
--HG--
extra : rebase_source : 90f79b6f4a2d8d925dd20eb0bf6ab96262c227d5
Ted Mielczarek