Tests for overflow when merging sampled profiles.

1- Merge profile having maximum counts with itself and verify overflow detected
RUN: llvm-profdata merge -sample %p/Inputs/overflow-sample.proftext %p/Inputs/overflow-sample.proftext -o %t.out 2>&1 | FileCheck %s -check-prefix=MERGE_OVERFLOW
RUN: llvm-profdata show -sample %t.out | FileCheck %s --check-prefix=SHOW_OVERFLOW
MERGE_OVERFLOW: {{.*}}: main: Counter overflow
SHOW_OVERFLOW: Function: main: 2000, 0, 2 sampled lines
SHOW_OVERFLOW-NEXT: Samples collected in the function's body {
SHOW_OVERFLOW-NEXT:   1: 1000, calls: _Z3bari:18446744073709551615
SHOW_OVERFLOW-NEXT:   2: 1000, calls: _Z3fooi:18446744073709551615
SHOW_OVERFLOW-NEXT: }
SHOW_OVERFLOW-NEXT: No inlined callsites in this function
SHOW_OVERFLOW-NEXT: Function: _Z3fooi: 18446744073709551615, 2000, 1 sampled lines
SHOW_OVERFLOW-NEXT: Samples collected in the function's body {
SHOW_OVERFLOW-NEXT:   1: 18446744073709551615
SHOW_OVERFLOW-NEXT: }
SHOW_OVERFLOW-NEXT: No inlined callsites in this function
SHOW_OVERFLOW-NEXT: Function: _Z3bari: 18446744073709551615, 2000, 1 sampled lines
SHOW_OVERFLOW-NEXT: Samples collected in the function's body {
SHOW_OVERFLOW-NEXT:   1: 18446744073709551615
SHOW_OVERFLOW-NEXT: }
SHOW_OVERFLOW-NEXT: No inlined callsites in this function

2- Merge profile having maximum counts by itself and verify no overflow
RUN: llvm-profdata merge -sample %p/Inputs/overflow-sample.proftext -o %t.out 2>&1 | FileCheck %s -allow-empty -check-prefix=MERGE_NO_OVERFLOW
RUN: llvm-profdata show -sample %t.out | FileCheck %s --check-prefix=SHOW_NO_OVERFLOW
MERGE_NO_OVERFLOW-NOT: {{.*}}: main: Counter overflow
SHOW_NO_OVERFLOW: Function: main: 1000, 0, 2 sampled lines
SHOW_NO_OVERFLOW-NEXT: Samples collected in the function's body {
SHOW_NO_OVERFLOW-NEXT:   1: 500, calls: _Z3bari:18446744073709551615
SHOW_NO_OVERFLOW-NEXT:   2: 500, calls: _Z3fooi:18446744073709551615
SHOW_NO_OVERFLOW-NEXT: }
SHOW_NO_OVERFLOW-NEXT: No inlined callsites in this function
SHOW_NO_OVERFLOW-NEXT: Function: _Z3fooi: 18446744073709551615, 1000, 1 sampled lines
SHOW_NO_OVERFLOW-NEXT: Samples collected in the function's body {
SHOW_NO_OVERFLOW-NEXT:   1: 18446744073709551615
SHOW_NO_OVERFLOW-NEXT: }
SHOW_NO_OVERFLOW-NEXT: No inlined callsites in this function
SHOW_NO_OVERFLOW-NEXT: Function: _Z3bari: 18446744073709551615, 1000, 1 sampled lines
SHOW_NO_OVERFLOW-NEXT: Samples collected in the function's body {
SHOW_NO_OVERFLOW-NEXT:   1: 18446744073709551615
SHOW_NO_OVERFLOW-NEXT: }
SHOW_NO_OVERFLOW-NEXT: No inlined callsites in this function