Fix LLVM 3.0 build issue.
Fix LLVM 3.0 build issue.

LLVM 3.0's raw_fd_ostream doesn't take an std::string as file name.

Bug swiftshader:123
Bug b/123193054

Change-Id: I994f6fe5ce98c573d4be48737934b7c6c0127434
Reviewed-on: https://swiftshader-review.googlesource.com/c/24088
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader