include: add msasn1.h (try 2)

[Austin English]

try 2:
remove WINAPI define
avoid (unsigned) long

For https://bugs.winehq.org/show_bug.cgi?id=38020

For reference, the header was based on mingw's:
https://github.com/Alexpux/mingw-w64/blob/master/mingw-w64-headers/include/msasn1.h
-- 
-Austin
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