py: Partially fix float to int conversion.

This fixes conversion when float type has more mantissa bits than small int,
and float value has small exponent. This is for example the case of 32-bit
platform using doubles, and converting value of time.time(). Conversion of
floats with larg exponnet is still not handled correctly.
diff --git a/py/objint_longlong.c b/py/objint_longlong.c
index ec55c77..5f48b71 100644
--- a/py/objint_longlong.c
+++ b/py/objint_longlong.c
@@ -40,6 +40,10 @@
 #include "runtime0.h"
 #include "runtime.h"
 
+#if MICROPY_PY_BUILTINS_FLOAT
+#include <math.h>
+#endif
+
 #if MICROPY_LONGINT_IMPL == MICROPY_LONGINT_IMPL_LONGLONG
 
 // Python3 no longer has "l" suffix for long ints. We allow to use it
@@ -187,6 +191,14 @@
     return o;
 }
 
+#if MICROPY_PY_BUILTINS_FLOAT
+mp_obj_t mp_obj_new_int_from_float(mp_float_t val) {
+    // TODO raise an exception if the unsigned long long won't fit
+    long long i = MICROPY_FLOAT_C_FUN(trunc)(val);
+    return mp_obj_new_int_from_ll(i);
+}
+#endif
+
 mp_obj_t mp_obj_new_int_from_str_len(const char **str, mp_uint_t len, bool neg, mp_uint_t base) {
     // TODO this does not honor the given length of the string, but it all cases it should anyway be null terminated
     // TODO check overflow