[MIR] Change test case to read from stdin instead of file
;CHECK: bb ;CHECK-NEXT: %namedVReg1353:_(p0) = COPY $d0
parts of the test case failed when the tests were placed in a directory
including "bb" in the path, since the full path of the file is then
output in the
; ModuleID = '/repo/bb/
line which the CHECK matched on and then the CHECK-NEXT failed.