msvc_recommended_pragmas.h: Silence C4819 warnings

msvc_recommended_pragmas.h: Silence C4819 warnings

This warning appears when unicode chars that cannot be displayed in the
current Windows code page is used anywhere in the file, including comment
blocks.  We probably don't need to see these, especially as problems
caused by such characters are manifested as other warnings or errors,
for example, the need to add BOM to a file when compiling code with
complex script on Windows.