Test the input file names overlap with the output file names.

This is OK for merging instrument profiles.
RUN: cp %S/Inputs/same-name-1.proftext %t.0.proftext
RUN: llvm-profdata merge -o %t.0.profdata -text %t.0.proftext %t.0.proftext
RUN: llvm-profdata show -counts -all-functions %t.0.profdata -o %t_show_0
RUN: llvm-profdata show -counts -all-functions %S/Inputs/same-name-2.proftext -o %t_show_1
RUN: diff %t_show_0 %t_show_1
RUN: llvm-profdata merge -o %t.1.profdata %S/Inputs/same-name-1.proftext
RUN: llvm-profdata merge -o %t.1.profdata %t.1.profdata %t.1.profdata
RUN: llvm-profdata show -counts -all-functions %t.1.profdata -o %t_show_2
RUN: diff %t_show_2 %t_show_1

We report error for the show command.
RUN: not llvm-profdata show -o %t.1.profdata %t.1.profdata 2>&1 | FileCheck %s
CHECK: llvm-profdata{{.*}} show: Input file name cannot be the same as the output file name!

This is OK for merging sample fdo profiles.
RUN: cp %S/Inputs/same-name-3.proftext %t.3.proftext
RUN: llvm-profdata merge --sample -o %t.3.profdata -text %t.3.proftext %t.3.proftext
RUN: llvm-profdata show --sample -counts -all-functions %t.3.profdata -o %t_show_3
RUN: llvm-profdata show --sample -counts -all-functions %S/Inputs/same-name-4.proftext -o %t_show_4
RUN: diff %t_show_3 %t_show_4
RUN: llvm-profdata merge --sample -o %t.5.profdata %S/Inputs/same-name-3.proftext
RUN: llvm-profdata merge --sample -o %t.5.profdata %t.5.profdata %t.5.profdata
RUN: llvm-profdata show --sample -counts -all-functions %t.5.profdata -o %t_show_6
RUN: diff %t_show_6 %t_show_4