test: fix x86_64-macos failures

This is just a temporary fix - I would like to unify all of x86_64
tests across linux and macos OSes.

test/incremental/x86_64-linux/assert_function.7.zig

@@ -0,0 +1,28 @@
+pub fn main() void {
+    var i: u32 = 0;
+    while (i < 4) : (i += 1) print();
+    assert(i == 4);
+}
+
+fn print() void {
+    asm volatile ("syscall"
+        :
+        : [number] "{rax}" (1),
+          [arg1] "{rdi}" (1),
+          [arg2] "{rsi}" (@ptrToInt("hello\n")),
+          [arg3] "{rdx}" (6),
+        : "rcx", "r11", "memory"
+    );
+}
+
+pub fn assert(ok: bool) void {
+    if (!ok) unreachable; // assertion failure
+}
+
+// run
+//
+// hello
+// hello
+// hello
+// hello
+//