OpenMP reductions not supported

Reproducer. Partial credits for the inspiration (all errors are mine): https://rookiehpc.org/openmp/docs/reduction/index.html

```Makefile
# Makefile
ENZLLD = ${HOME}/repositories/ENZYME/Enzyme-v0.0.180/enzyme/build-v0.0.180/Enzyme/LLDEnzyme-20.so

run: issue.exe
./$?

issue.exe: issue.o
clang -fopenmp=libomp $? -o $@ -v -fuse-ld=lld -flto -Wl,--load-pass-plugin=$(ENZLLD)

issue.o: issue.c
clang -fopenmp=libomp -flto -c issue.c

clean:
rm *.o *.exe
```

```c
// issue.c
#include
#include
#include

double __enzyme_autodiff(void*, ...);
extern int enzyme_const, enzyme_dup, enzyme_out;

double compute(double* myArray, const int ARRAY_SIZE) {
// Calculate the sum of all elements
double sum = 0;
#pragma omp parallel for default(none) shared(myArray) firstprivate(ARRAY_SIZE) reduction(+: sum)
for(int i = 0; i < ARRAY_SIZE; i++)
{
sum += myArray[i];
}
return sum;
}

int main(int argc, char* argv[])
{
// Use 2 threads when creating OpenMP parallel regions
omp_set_num_threads(2);

double total = 0;
const int ARRAY_SIZE = 10;
double* myArray = malloc(sizeof(double) * ARRAY_SIZE);
double* myArray_der = malloc(sizeof(double) * ARRAY_SIZE);
if(myArray_der == NULL)
{
printf("Cannot allocate the array \"myArray\".\n");
return EXIT_FAILURE;
}

// Initialise the array
for(int i = 0; i < ARRAY_SIZE; i++)
{
myArray[i] = i;
myArray_der[i] = 0;
}

total = compute(myArray, ARRAY_SIZE);
printf("The sum of all array elements is equal to %f.\n", total);

__enzyme_autodiff((void*)compute,
enzyme_dup, myArray, myArray_der,
enzyme_const, ARRAY_SIZE - 1);

printf("The derivative of the sum of the array elements is equal to:\n");
for(int i = 0; i < ARRAY_SIZE; i++)
{
printf("%f, ", myArray_der[i]);
}
printf("\n");
printf("Note last element is zero because we passed ARRAY_SIZE - 1\n");

free(myArray);
free(myArray_der);

return EXIT_SUCCESS;
}
```

Works fine once one removes OpenMP.