ROOT doesn't compile with gcc-15

[hageboeck]

Check duplicate issues.

• Checked for duplicates

Description

Starting from gcc-15, <cstdint> needs to be included when fixed-size integer types are used.
See also:
https://bugs.gentoo.org/942438

In ROOT, there is currently four places that create problems:

• Two throughout ROOT (Fix two includes to compile with gcc-15 #17443)
• Two in the interpreter.
  LLVM fixed those here 7e44305 and as a side effect here 2222fdd. The former applies cleanly, but the latter doesn't.
  Update: We can backport Add missing include to X86MCTargetDesc.h llvm/llvm-project#123320 instead of 2222fdd if the PR gets merged. llvm/llvm-project@7abf440
  Update 2: This is now [llvm-project] Backport fix for compilation issue with gcc-15 #17510
• One more location found by mellert: Fixes for compiling with GCC 15 (Fedora 42) #17455

What could be the solutions to make ROOT compile cleanly?

1. Wait until the llvm upgrade?
2. Patch llvm ourselves until the upgrade?
3. Pull in already now the commits from llvm-main? (the latter doesn't apply, though)

@devajithvs @hahnjo @amadio

Reproducer

Compile ROOT with gcc-15

ROOT version

Master, but also 6.34, 6.32 as can be seen in the gentoo bug report

Installation method

Source

Operating system

Gentoo

Additional context

No response

[hahnjo]

LLVM fixed those here and as a side effect here. The former applies cleanly, but the latter doesn't.

The first one we can backport. For the second one, as the header llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.h uses the fixed-size integer types directly, it should include <cstdint> directly and not transitively via llvm/ADT/SmallVector.h. This should be fixed upstream (regardless of it being fixed as a side effect) and then we can backport that.

[hageboeck]

One more location found by mellert: #17455