[clang] clang/limits.h: Avoid including limits.h twice (PR #120526)

[YunQiang Su via cfe-commits]

wzssyqa wrote:

> Do you get the same behavior when you use `-isystem` instead?

There is no warning then if I use command
```
clang -E -I build-x86/ -I sysdeps/x86 -I. -isystem ./include -I sysdeps/unix/sysv/linux/ -I sysdeps/generic/ -include include/libc-symbols.h -O2 -H xx.c
```
instead of 
```
clang -E -I build-x86/ -I sysdeps/x86 -I. -I ./include -I sysdeps/unix/sysv/linux/ -I sysdeps/generic/ -include include/libc-symbols.h -O2 -H xx.c
```


The content of `xx.c` is
```
#include <limits.h>
```

https://github.com/llvm/llvm-project/pull/120526