Visual Studio has had stdint.h since its 2010 edition. Before that there were readily-available substitutes (like https://code.google.com/p/msinttypes/), or you could do it yourself by typedef'ing [unsigned] __intNN as [u]intNN_t.
But not stdbool, nor a lot of other C99-ish features until Visual Studio 2013 Update 4 which shipped this past November. 10 or 15 years too long makes little difference. Way too long over due.
Somebody elsewhere pointed out to me that these will give types that are not aliases of the common ones. I.e. __int8 isn't the same as either unsigned char or char. Probably won't make a difference most places, but what does?
That is also the case in usual implementations of stdint.h, where int8_t is defined to be `signed char`. In C and C++, `char`, `signed char`, and `unsigned char` are different types, and `char` is not guaranteed to be signed or unsigned---that's up to the implementation.
EDIT: looking at the documentation, it appears that __int8 is supposed to always be an alias for `char`, even as far back as 2003: https://msdn.microsoft.com/en-us/library/29dh1w7z(v=vs.71).a.... However, the workaround found in msinttypes suggests that Visual Studio 6 does have this problem. I weep for those still using it.
