[flang][runtime] Correct RANDOM_INIT seed generation (#106250)

The initial seed was generated from a bitwise AND ("&") of two
clock-generated values, instead of an XOR or (best) a truncated integer
multiplication. Maybe I mistyped a shift-7 instead of a shift-6 or
shift-8 when I wrote that line, but it was most likely just stupidity.

Fixes #106221.

flang/runtime/random.cpp

@@ -42,7 +42,7 @@ void RTNAME(RandomInit)(bool repeatable, bool /*image_distinct*/) {
 #ifdef CLOCK_REALTIME
       timespec ts;
       clock_gettime(CLOCK_REALTIME, &ts);
-      generator.seed(ts.tv_sec & ts.tv_nsec);
+      generator.seed(ts.tv_sec ^ ts.tv_nsec);
 #else
       generator.seed(time(nullptr));
 #endif