Add some missing #includes.

My experimental build with clang-cl at -Wall did show up a few things
that are safe enough to fix right now. One was this list of missing
includes, which was causing a lot of -Wmissing-prototype warnings, and
is a real risk because it means the declarations in headers weren't
being type-checked against the actual function definitions.

Happily, no actual mismatches.

keygen/mpunsafe.c

@@ -7,6 +7,7 @@
 #include "puttymem.h"
 
 #include "mpint.h"
+#include "mpunsafe.h"
 #include "crypto/mpint_i.h"
 
 /*