[clang][test] Try to fix Sema/format-strings.c on i686 (#181800)
https://github.com/llvm/llvm-project/pull/180566 did this for 32bit arm,
but this still breaks for us downstream on i686 with:
```
# .---command stderr------------
# | error: 'expected-warning' diagnostics expected but not seen:
# | File /builddir/build/BUILD/llvm-project/clang/test/Sema/format-strings.c Line 990: format specifies type 'size_t' (aka '{{.+}}') but the argument has type '_Bool'
# | File /builddir/build/BUILD/llvm-project/clang/test/Sema/format-strings.c Line 991: format specifies type 'ptrdiff_t' (aka '{{.+}}') but the argument has type '_Bool'
# | 2 errors generated.
# `-----------------------------
```