VS: Properly quote arguments in nasm.xml
Most arguments were quoted, but some weren't, causing problems if the arguments contained whitespace.
In particular, the _STL_EXTRA_DISABLED_WARNINGS value takes spaces and CMake's NASM support applies all add_definitions lines to NASM. The -D flag is missing quotes, so projects using NASM and setting _STL_EXTRA_DISABLED_WARNINGS break in the Visual Studio generator.
Likewise, the -o flag is missing quotes, which means filenames with spaces do not work.
(The -U flag is unlikely to need quotes, but include them for consistency.)
Extend the existing VSNASM test to cover these cases.