PATCH win32/mingw32: jcf_open_exact_case prototype

[Andrew Haley]

Aaron W. LaFramboise writes:
 > I've been applying the following patch to fix a no previous prototype
 > warning that causes bootstrap to fail at werror.  Including the header
 > that prototypes jcf_open_exact_case causes lots of undefined symbol
 > warnings, and so it seems this is not the way to do this, so I just
 > simply prototype the function near the other file prototypes.
 > 
 > I don't know if this is the right way to fix this warning.

Mohan, could you please sort this out?

Andrew.