[BOLT] Fix heatmaps on large BOLTE'd binaries.

Large binaries get two text segments mapped when loaded in memory.
BOLT processes only the first, which is not having a correct BaseAddress,
causing a wrong computation of a BinaryMMapInfo's size.

Consequently, BOLT wrongly thinks that many of the samples fall outside
the binary and ignores them. As a result, the computed heatmap is
incomplete, and the section hotness statistics are wrong.

This bug is present in both the AArch64 and x86 backends.

---

This patch introduces flag 'perf-script-events' that allows passing
perf events without BOLT having to parse them using 'perf script'.
The flag is used to pass a mock perf profile that has two memory
mappings for a mock binary that has two text segments. The size of the
mapping is updated as `parseMMapEvents` now processes all text segments.

---

Example used in unit tests:
From `/proc/<BINARY PID>/maps`, we have 2 text mappings, say A and B.

```
abc0000000-abc1000000 r-xp 011c0000 103:01 1573523 BINARY
abc2000000-abca000000 r-xp 031d0000 103:01 1573523 BINARY
```

Size of text mappings:

| Mapping |  Size  |
| ------- | ------ |
| A       | ~15MB  |
| B       | ~135MB |

---

Example on a real program:
```
2f7200000-2fabca000 r--p 00000000        bolted-binary
2fabd9000-2fe47c000 r-xp 039c9000        bolted-binary <- 1st txt segment
2fe48b000-2fe61d000 r--p 0727b000        bolted-binary
2fe62c000-2fe660000 rw-p 0740c000        bolted-binary
2fe660000-2fea4c000 rw-p 00000000
2fec00000-303dad000 r-xp 07a00000        bolted-binary <- 2nd (appears only on the bolted binary)
```

Author: paschalis-mpeis

bolt/lib/Profile/DataAggregator.cpp

@@ -2017,15 +2017,6 @@ std::error_code DataAggregator::parseMMapEvents() {
     if (FileMMapInfo.first == "(deleted)")
       continue;
 
-    // Consider only the first mapping of the file for any given PID
-    auto Range = GlobalMMapInfo.equal_range(FileMMapInfo.first);
-    bool PIDExists = llvm::any_of(make_range(Range), [&](const auto &MI) {
-      return MI.second.PID == FileMMapInfo.second.PID;
-    });
-
-    if (PIDExists)
-      continue;
-
     GlobalMMapInfo.insert(FileMMapInfo);
   }
 
@@ -2076,12 +2067,18 @@ std::error_code DataAggregator::parseMMapEvents() {
                << " using file offset 0x" << Twine::utohexstr(MMapInfo.Offset)
                << ". Ignoring profile data for this mapping\n";
         continue;
-      } else {
-        MMapInfo.BaseAddress = *BaseAddress;
       }
+      MMapInfo.BaseAddress = *BaseAddress;
     }
 
+    // Try to add MMapInfo to the map and update its size. Large binaries
+    // may span multiple text segments, so the mapping is inserted only on the
+    // first occurrence. If a larger section size is found, it will be updated.
     BinaryMMapInfo.insert(std::make_pair(MMapInfo.PID, MMapInfo));
+    uint64_t EndAddress = MMapInfo.MMapAddress + MMapInfo.Size;
+    uint64_t Size = EndAddress - BinaryMMapInfo[MMapInfo.PID].BaseAddress;
+    if (Size > BinaryMMapInfo[MMapInfo.PID].Size)
+      BinaryMMapInfo[MMapInfo.PID].Size = Size;
   }
 
   if (BinaryMMapInfo.empty()) {