test.c:

struct {
    long long a;
    char b;
} c;

If you compile it with clang -target x86_64-unknown-linux-elf -Wpadded -c test.c you get the warning test.c:1:1: warning: padding size of 'struct (unnamed at test.c:1:1)' with 7 bytes to alignment boundary [-Wpadded] as expected.

However, if you target MS abi with clang -target x86_64-unknown-windows-coff -Wpadded -c test.c there is no warning at all. Note that it happens in real code too, where the struct is actually used. This is just a minimal example.