[X86][FastISel] Add missing flag -fast-isel-abort to run lines in test fast-isel-fptrunc-fpext.ll.

Flag -fast-isel-abort is required in order to verify that X86FastISel
never fails to select FPExt (float-to-double) and FPTrunc (double-to-float).
No Functional change intended.

llvm-svn: 229489