x87: should evaluate function calls like fabs and pow for constant arguments

Subject: https://github.com/rfalke/decompiler-subjects/blob/master/from_holdec/i386_x87_fpu/ia32_elf/subject.exe
Output:
```
int32_t FABS(int32_t a1) {
float64_t v1 = fabs((float64_t)(int64_t)a1);
printf("FABS(para): should= is=%12f/%15e\n", v1, v1);
float64_t v2 = fabsl(-1.0L); // 0x8049f56
printf("FABS(-1): should= 1.000000/ 1.000000e+00 is=%12f/%15e\n", v2, v2);
printf("FABS(-0): should= 0.000000/ 0.000000e+00 is=%12f/%15e\n", 0.0, 0.0);
printf("FABS(+1): should= 1.000000/ 1.000000e+00 is=%12f/%15e\n", 1.0, 1.0);
return 0;
}
```

For -0 and +1 there is no fabs call but not so for -1.0. "fabsl(-1.0L)" should be replaced with "1.0".

Start by reproducing the decompiler output from subject.exe and inspect the generated FABS function, especially the fabsl(-1.0L) expression. Trace the constant-evaluation path for floating-point function calls such as fabs and pow; done means the constant argument is evaluated and the output contains 1.0 rather than fabsl(-1.0L).

Written by the indexing model from the issue text.