[RISCV][GISel] Do libcall for G_FPTOSI, G_FPTOUI when no D or F support (#94613)

When compiling the following code:
```cpp
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdbool.h>

int main() {
    int a;
    float f;
    scanf("%d", &a);

    scanf("%f", &f);
    a += (int)f;
    
    return a;
}
``` 
for `-march=rv32ima_zbb` we get a libcall:
```
call    scanf
        lw      a0, -20(s0)
        call    __fixsfsi
        mv      a1, a0
```
When we try to use GlobalISel we get this error:
```
 error in backend: unable to legalize instruction: %9:_(s32) = G_FPTOSI %8:_(s32) (in function: main)
```

(Here is a link to a reproducer in Godblot:
https://godbolt.org/z/f67vEEb41 )

The goal of this PR is to do a libcall for the legalization of
`G_FPTOSI` and `G_FPTOUI` instead of doing a fallback to Selection DAG
to do the same libcall later.

Author: spaits

llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.cpp

@@ -409,7 +409,8 @@ RISCVLegalizerInfo::RISCVLegalizerInfo(const RISCVSubtarget &ST)
   getActionDefinitionsBuilder({G_FPTOSI, G_FPTOUI})
       .legalIf(all(typeInSet(0, {s32, sXLen}), typeIsScalarFPArith(1, ST)))
       .widenScalarToNextPow2(0)
-      .clampScalar(0, s32, sXLen);
+      .clampScalar(0, s32, sXLen)
+      .libcall();
 
   getActionDefinitionsBuilder({G_SITOFP, G_UITOFP})
       .legalIf(all(typeIsScalarFPArith(0, ST), typeInSet(1, {s32, sXLen})))