Merge pull request libgit2#6373 from christoph-cullmann/fix_compile_WIN32_LEAN_AND_MEAN

fix compile on Windows with -DWIN32_LEAN_AND_MEAN

Author: ethomson

src/util/rand.c

@@ -14,6 +14,10 @@ See <http://creativecommons.org/publicdomain/zero/1.0/>. */
 # include <sys/random.h>
 #endif
 
+#if defined(GIT_WIN32)
+# include <wincrypt.h>
+#endif
+
 static uint64_t state[4];
 static git_mutex state_lock;