[llvm][dwarfdump] Add --child-tags option to filter by DWARF tags (#165720)
This patch adds a new option `--child-tags` (`-t` for short), which
makes dwarfdump only dump children whose DWARF tag is in the list of
tags specified by the user.
Motivating examples are:
* dumping all global variables in a CU
* dumping all non-static data members of a structure
* dumping all module import declarations of a CU
* etc.
For tags not known to dwarfdump, we pretend that the tag wasn't
specified.
Note, this flag only takes effect when `--show-children` is set (either
explicitly or implicitly). We error out when trying to use the flag
without dumping children.
Example:
```
$ builds/release/bin/llvm-dwarfdump -t DW_TAG_structure_type a.out.dSYM
...
0x0000000c: DW_TAG_compile_unit
DW_AT_producer ("clang version 22.0.0git (git@github.com:Michael137/llvm-project.git 737da3347c2fb01dd403420cf83e9b8fbea32618)")
DW_AT_language (DW_LANG_C11)
...
0x0000002a: DW_TAG_structure_type
DW_AT_APPLE_block (true)
DW_AT_byte_size (0x20)
0x00000067: DW_TAG_structure_type
DW_AT_APPLE_block (true)
DW_AT_name ("__block_descriptor")
DW_AT_byte_size (0x10)
...
```
```
$ builds/release/bin/llvm-dwarfdump -t DW_TAG_structure_type -t DW_TAG_member a.out.dSYM
...
0x0000000c: DW_TAG_compile_unit
DW_AT_producer ("clang version 22.0.0git (git@github.com:Michael137/llvm-project.git 737da3347c2fb01dd403420cf83e9b8fbea32618)")
DW_AT_language (DW_LANG_C11)
DW_AT_name ("macro.c")
...
0x0000002a: DW_TAG_structure_type
DW_AT_APPLE_block (true)
DW_AT_byte_size (0x20)
0x0000002c: DW_TAG_member
DW_AT_name ("__isa")
DW_AT_type (0x00000051 "void *")
DW_AT_data_member_location (0x00)
0x00000033: DW_TAG_member
DW_AT_name ("__flags")
DW_AT_type (0x00000052 "int")
DW_AT_data_member_location (0x08)
0x0000003a: DW_TAG_member
DW_AT_name ("__reserved")
DW_AT_type (0x00000052 "int")
DW_AT_data_member_location (0x0c)
0x00000041: DW_TAG_member
DW_AT_name ("__FuncPtr")
DW_AT_type (0x00000056 "void (*)(int)")
DW_AT_data_member_location (0x10)
0x00000048: DW_TAG_member
DW_AT_name ("__descriptor")
DW_AT_type (0x00000062 "__block_descriptor *")
DW_AT_alignment (8)
DW_AT_data_member_location (0x18)
0x00000067: DW_TAG_structure_type
DW_AT_APPLE_block (true)
DW_AT_name ("__block_descriptor")
DW_AT_byte_size (0x10)
0x0000006a: DW_TAG_member
DW_AT_name ("reserved")
DW_AT_type (0x00000079 "unsigned long")
DW_AT_data_member_location (0x00)
0x00000071: DW_TAG_member
DW_AT_name ("Size")
DW_AT_type (0x00000079 "unsigned long")
DW_AT_data_member_location (0x08)
...
```
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