[Bug preprocessor/91932] New: #pragma does not silence floating constant overflow warnings

[lh_mouse at 126 dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91932

            Bug ID: 91932
           Summary: #pragma does not silence floating constant overflow
                    warnings
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: preprocessor
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lh_mouse at 126 dot com
  Target Milestone: ---

### Testcase 1:

```c
#pragma GCC diagnostic ignored "-Woverflow"
double x = 1.0e10000;
```
results in
```
prog.cc:2:1: warning: floating constant exceeds range of 'double' [-Woverflow]
    2 | double x = 1.0e10000;
      | ^~~~~~
```


### Testcase 2:  <https://wandbox.org/permlink/Qcck5DvbLwOu9Ls3>

```c
#pragma GCC diagnostic ignored "-Woverflow"

#define CONS(a,b)  1.0##e##a##b

int main()
  {
    double x = CONS(-,10000);
    double y = CONS(+,10000);
    (void)(x+y);
  }
```
results in:
```
prog.cc:7:3: warning: floating constant truncated to zero [-Woverflow]
    7 |   double x = CONS(-,10000);
      |   ^~~~~~
prog.cc:8:3: warning: floating constant exceeds range of 'double' [-Woverflow]
    8 |   double y = CONS(+,10000);
      |   ^~~~~~
```


This overflow/underflow is intended sometimes.