Recently, we have been looking at some optimizations targeting
individual calls. In particular, we plan to extend the address mapping
technique to map to individual callsites. For example, in this piece of
code for a basic blocks:

```
<BB>:
1200:    lea 0x1(%rcx), %rdx
1204:    callq foo
1209:    cmpq 0x10, %rdx
120d:    ja  L1
```

We want to emit 0x9 as the call site offset for `callq foo` (the offset
from the block entry to right after the call), so that we know if a
sampled address is before the call or after.

This PR implements the decode/encode/emit capability. The Codegen change
will be implemented in a later PR.

This removes unused variables and dead code in the method.

All notes in the note section must be correctly aligned, including the
first. The tool should refuse to generate notes if the section offset is
incorrect in this respect.

This relands #118157 with a fix for the use of an uninitialized
variable and additional tests.

The System V ABI
(https://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section)
states that the note entries and their descriptor fields must be aligned
to 4 or 8 bytes for 32-bit or 64-bit objects respectively. In practice,
64-bit systems can use both alignments, with the actual format being
determined by the alignment of the segment. For example, the Linux
gABI extension (https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf)
contains a special note on this, see 2.1.7 "Alignment of Note Sections".

This patch adjusts the format of the generated notes to the specified
section alignment. Since `llvm-readobj` was fixed in a similar way in
https://reviews.llvm.org/D150022, "[Object] Fix handling of Elf_Nhdr
with sh_addralign=8", the generated notes can now be parsed
successfully by the tool.

This reverts commit 1724188c19f363c877fcf1bca86d92af3864b338.

Some build bots reported a failure in the updated test

The [System V ABI](https://www.sco.com/developers/gabi/latest/ch5.pheader.html#note_section)
states that the note entries and their descriptor fields must be aligned
to 4 or 8 bytes for 32-bit or 64-bit objects respectively. In practice,
64-bit systems can use both alignments, with the actual format being
determined by the alignment of the segment. For example, the
[Linux gABI extension](https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf)
contains a special note on this, see 2.1.7 "Alignment of Note Sections".

This patch adjusts the format of the generated notes to the specified
section alignment. Since `llvm-readobj` was fixed in a similar way in
[D150022](https://reviews.llvm.org/D150022), "[Object] Fix handling of
Elf_Nhdr with sh_addralign=8", the generated notes can now be parsed
successfully by the tool.

Sometimes we want to use a `PgoAnalysisMap` feature that doesn't require
the BB entries info, e.g. only the `FuncEntryCount`, but the BB entries
is emitted by default, so I'm adding an option to skip the info for this
case to save the binary size(can save ~90% size of the section). For
implementation, it extends a new field(`OmitBBEntries`) in
`BBAddrMap::Features` for this and it's controlled by a switch
`--basic-block-address-map-skip-bb-entries`.

Note that this naturally supports backwards compatibility as the field
is zero for the old version, matches the decoding in the new version
llvm.

Identified with misc-include-cleaner.