Unix: add machine-specific sqrt support.

unix/main.c

@@ -176,3 +176,9 @@ int main(int argc, char **argv) {
     //printf("total bytes = %d\n", m_get_total_bytes_allocated());
     return 0;
 }
+
+// for sqrt
+#include <math.h>
+machine_float_t machine_sqrt(machine_float_t x) {
+    return sqrt(x);
+}

unix/mpyconfig.h

@@ -14,3 +14,5 @@ typedef int64_t machine_int_t; // must be pointer size
 typedef uint64_t machine_uint_t; // must be pointer size
 typedef void *machine_ptr_t; // must be of pointer size
 typedef double machine_float_t;
+
+machine_float_t machine_sqrt(machine_float_t x);