Test the profile version.

RUN: llvm-profdata merge -o %t.profdata %p/Inputs/basic.proftext
RUN: llvm-profdata show --profile-version %t.profdata | FileCheck %s
CHECK: Profile version: 13

RUN: llvm-profdata merge -o %t.prev.profdata %p/Inputs/basic.proftext --write-prev-version
RUN: llvm-profdata show --profile-version %t.prev.profdata | FileCheck %s --check-prefix=PREV
PREV: Profile version: 11