Module: keep frame pointer in ReleaseSmall on x86

[ghost]

On x86 and x86_64 keeping the frame pointer usually reduces binary size, even for simple programs:

~$ cat x.zig
pub fn main() void {
    @import("std").debug.print("hello", .{});
}
~$ zig build-exe x.zig -target x86_64-linux -OReleaseSmall -fno-omit-frame-pointer && wc -c x
5168 x
~$ zig build-exe x.zig -target x86_64-linux -OReleaseSmall -fomit-frame-pointer && wc -c x
5216 x

~$ cat x.zig
pub fn main() void {
    @import("std").debug.print("hello", .{});
}
~$ zig build-exe x.zig -target x86-linux -OReleaseSmall -fno-omit-frame-pointer && wc -c x
3400 x
~$ zig build-exe x.zig -target x86-linux -OReleaseSmall -fomit-frame-pointer && wc -c x
3556 x

A bigger benchmark is the Zig compiler:

With no changes to anything on master branch:

$ zig build -Dno-lib -Dno-langref --zig-lib-dir lib -Doptimize=ReleaseSmall
$ wc -c zig-out/bin/zig
10698792 zig-out/bin/zig

Adding .omit_frame_pointer = false in addCompilerStep in build.zig:

$ zig build -Dno-lib -Dno-langref --zig-lib-dir lib -Doptimize=ReleaseSmall
$ wc -c zig-out/bin/zig
10155744 zig-out/bin/zig

x86 seems to be a bit of a special case. I couldn't find any other architecture where this reduces binary size.

Progress towards #22270

[andrewrk]

Thanks!