[Matrix] Support #pragma clang fp

From https://bugs.llvm.org/show_bug.cgi?id=49739:

Currently, `#pragma clang fp` are ignored for matrix types.

For the code below, the `contract` fast-math flag should be added to the generated call to `llvm.matrix.multiply` and `fadd`

```
typedef float fx2x2_t __attribute__((matrix_type(2, 2)));

void foo(fx2x2_t &A, fx2x2_t &C, fx2x2_t &B) {
  #pragma clang fp contract(fast)
  C = A*B + C;
}
```

Reviewed By: fhahn, mibintc

Differential Revision: https://reviews.llvm.org/D100834