compilation: pass omit_frame_pointer through to builtin.zig

Renamed dwarf_unwinding -> stack_iterator to better reflect that it's not just DWARF unwinding.
Added a test for unwinding with a frame pointer.

test/standalone/stack_iterator/shared_lib_unwind.zig

@@ -0,0 +1,43 @@
+const std = @import("std");
+const debug = std.debug;
+const testing = std.testing;
+
+noinline fn frame4(expected: *[5]usize, unwound: *[5]usize) void {
+    expected[0] = @returnAddress();
+
+    var context: debug.ThreadContext = undefined;
+    testing.expect(debug.getContext(&context)) catch @panic("failed to getContext");
+
+    var debug_info = debug.getSelfDebugInfo() catch @panic("failed to openSelfDebugInfo");
+    var it = debug.StackIterator.initWithContext(expected[0], debug_info, &context) catch @panic("failed to initWithContext");
+    defer it.deinit();
+
+    for (unwound) |*addr| {
+        if (it.next()) |return_address| addr.* = return_address;
+    }
+}
+
+noinline fn frame3(expected: *[5]usize, unwound: *[5]usize) void {
+    expected[1] = @returnAddress();
+    frame4(expected, unwound);
+}
+
+fn frame2(expected: *[5]usize, unwound: *[5]usize) callconv(.C) void {
+    expected[2] = @returnAddress();
+    frame3(expected, unwound);
+}
+
+extern fn frame0(
+    expected: *[5]usize,
+    unwound: *[5]usize,
+    frame_2: *const fn (expected: *[5]usize, unwound: *[5]usize) callconv(.C) void,
+) void;
+
+pub fn main() !void {
+    if (!std.debug.have_ucontext or !std.debug.have_getcontext) return;
+
+    var expected: [5]usize = undefined;
+    var unwound: [5]usize = undefined;
+    frame0(&expected, &unwound, &frame2);
+    try testing.expectEqual(expected, unwound);
+}