On Win7 32bits, when CMake targets "Visual Studio 10 Win64", the build fails with the warnings below:

..\src\hash.c(65): warning C4267: 'function' : conversion from 'size_t' to 'unsigned long', possible loss of data
..\src\indexer.c(153): warning C4267: 'function' : conversion from 'size_t' to 'unsigned int', possible loss of data
..\src\indexer.c(369): warning C4267: 'function' : conversion from 'size_t' to 'int', possible loss of data
..\src\indexer.c(374): warning C4267: 'function' : conversion from 'size_t' to 'uInt', possible loss of data
..\src\netops.c(109): warning C4244: '=' : conversion from 'SOCKET' to 'int', possible loss of data
..\src\pack.c(423): warning C4244: '+=' : conversion from '__int64' to 'off_t', possible loss of data
..\src\path.c(42): warning C4244: '=' : conversion from '__int64' to 'int', possible loss of data
..\src\pkt.c(203): warning C4244: '=' : conversion from 'ssize_t' to 'int', possible loss of data
..\src\refs.c(214): warning C4267: 'initializing' : conversion from 'size_t' to 'const unsigned int', possible loss of data
..\src\tag.c(156): warning C4244: '=' : conversion from '__int64' to 'unsigned int', possible loss of data
..\src\transport_git.c(467): warning C4267: '+=' : conversion from 'size_t' to 'off_t', possible loss of data
..\src\tsort.c(161): warning C4244: 'initializing' : conversion from 'ssize_t' to 'const int', possible loss of data
..\tests\t00-core.c(59): warning C4306: 'type cast' : conversion from 'int' to 'void *' of greater size

This MSDN article gives some hints about this topic.