Windows MSVC port

Extend the windows port so it compiles with the toolchain from Visual Studio 2013
diff --git a/py/mpz.c b/py/mpz.c
index d6eca30..8eed283 100644
--- a/py/mpz.c
+++ b/py/mpz.c
@@ -1092,8 +1092,11 @@
 */
 mpz_t *mpz_lcm(const mpz_t *z1, const mpz_t *z2)
 {
-    if (z1->len == 0 || z2->len == 0)
-        return mpz_zero();
+    // braces below are required for compilation to succeed with CL, see bug report

+    // https://connect.microsoft.com/VisualStudio/feedback/details/864169/compilation-error-when-braces-are-left-out-of-single-line-if-statement

+    if (z1->len == 0 || z2->len == 0) {

+        return mpz_zero();

+    }
 
     mpz_t *gcd = mpz_gcd(z1, z2);
     mpz_t *quo = mpz_zero();