Add $$select. "--fp-math" options. Fixed issue with accidentally silent error on failed vector conversions.

test/unit/regression/select.c3

@@ -0,0 +1,10 @@
+import std;
+fn long[<4>] process(long[<4>] a, long[<4>] b) @noinline
+{
+	return math::select({ true, true, false, true }, a, b);
+}
+fn void test_select() @test
+{
+	long[<4>] res = process({ 4, 5, 6, 7 }, { 100, 200, 300, 400 });
+	assert(res == { 4, 5, 300, 7});
+}