MSVC.README.rst: Update VS 2008/x64 build notes

It appears that tests/repository/gitypelibtest.c needs to be added to
the list of files that we must change the optimization flag from /O2 to
/O1 in order that the Visual Studio 2008 x64 compiler does not hang, due
to compiler optimization issues.
5 jobs for gnome-3-32 in 7 minutes and 58 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #290110
fedora-x86_64-autotools

00:02:43

passed #290109
fedora-x86_64-meson

00:01:19

passed #290112
win32
msys2-mingw32-autotools

00:07:28

passed #290111
win32
msys2-mingw32-meson

00:03:10

passed #290113
win32
vs2017-x64-meson

00:04:46