std.testing: don't ask wasm to stack trace

Author: andrewrk

lib/std/testing.zig

@@ -17,7 +17,7 @@ var base_allocator_instance = std.heap.FixedBufferAllocator.init("");
 /// This should only be used in temporary test programs.
 pub const allocator = allocator_instance.allocator();
 pub var allocator_instance: std.heap.GeneralPurposeAllocator(.{
-    .stack_trace_frames = 10,
+    .stack_trace_frames = if (std.debug.sys_can_stack_trace) 10 else 0,
     .resize_stack_traces = true,
     // A unique value so that when a default-constructed
     // GeneralPurposeAllocator is incorrectly passed to testing allocator, or