[X86][FastISel] Support materializing floating-point constants for large code model & PIC

The following program miscompiles because rL216012 added static
relocation model support but not for PIC.

```
// clang -fpic -mcmodel=large -O0 a.cc
double foo() { return 42.0; }
```

This patch adds PIC support.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D86024