re-enable code coverage + enzyme

@chapman39 is already working on this.

Since Oct 10, 2025.

Enzyme does not work well with code coverage.

```cpp
#include
extern "C" double __enzyme_autodiff(void*, double);

double square(double x) {
return x * x;
}

double dsquare(double x) {
// This returns the derivative of square, i.e., 2 * x
return __enzyme_autodiff((void*)square, x);
}

int main() {
for (double i = 1; i < 5; ++i) {
std::cout << "square(" << i << ") = " << square(i)
<< ", dsquare(" << i << ") = " << dsquare(i) << std::endl;
}
return 0;
}
```

Link with Enzyme and `--coverage` CXX flags, and you will get the following error:

```
root@50e20fa2bc58:/home/serac/serac_repo/enzyme_cov# clang++ -fplugin=../Enzyme/enzyme/build1/Enzyme/ClangEnzyme-19.so -fprofile-instr-generate -fcoverage-mapping ./enzyme_smoketest.cpp
error: Enzyme: ; Function Attrs: mustprogress noinline nounwind optnone willreturn uwtable
define dso_local noundef double @preprocess__Z6squared(double noundef %0) #5 {
%2 = load i64, ptr @__profc__Z6squared, align 8
%3 = add i64 %2, 1
store i64 %3, ptr @__profc__Z6squared, align 8
%4 = fmul double %0, %0
ret double %4
}

constantarg[double %0] = 0 type: {[-1]:Float@double} - vals: {}
constantinst[ %2 = load i64, ptr @__profc__Z6squared, align 8] = 0 val:0 type: {}
constantinst[ %3 = add i64 %2, 1] = 0 val:0 type: {}
constantinst[ store i64 %3, ptr @__profc__Z6squared, align 8] = 0 val:1 type: {}
constantinst[ %4 = fmul double %0, %0] = 0 val:0 type: {[-1]:Float@double}
constantinst[ ret double %4] = 1 val:1 type: {}
cannot handle unknown binary operator: %3 = add i64 %2, 1

1 error generated.
```

According to an issue in Enzyme, if you re-build Enzyme with coverage CXX flags, it'll work. However, after doing so and creating a small CMake reproducer, I was not able to get it working.

Related issue: https://github.com/EnzymeAD/Enzyme/issues/2411