[clang] [llvm] [CMake] Preserve clang-prebolt (PR #109351)

[Amir Ayupov via cfe-commits]

aaupov wrote:

> This commit is breaking LTO-PGO-BOLT build while optimizing clang with BOLT. 
> 
> 
> 
> ```
> 
> [3064/3065] Merging BOLT fdata
> 
> Using legacy profile format.
> 
> Profile from 2 files merged.
> 
> [3064/3065] Optimizing Clang with BOLT
> 
> BOLT-INFO: shared object or position-independent executable detected
> 
> BOLT-INFO: Target architecture: aarch64
> 
> BOLT-INFO: BOLT version: 51d1d03b17bb8bf66b6422c4482d8d615ab53409
> 
> BOLT-INFO: first alloc address is 0x0
> 
> BOLT-INFO: enabling relocation mode
> 
> BOLT-INFO: pre-processing profile using branch profile reader
> 
> BOLT-WARNING: 1 collisions detected while hashing binary objects. Use -v=1 to see the list.
> 
> BOLT-INFO: number of removed linker-inserted veneers: 0
> 
> BOLT-INFO: 11906 out of 212101 functions in the binary (5.6%) have non-empty execution profile
> 
> BOLT-INFO: 272 functions with profile could not be optimized
> 
> BOLT-INFO: profile for 1 objects was ignored
> 
> BOLT-INFO: removed 1 empty block
> 
> BOLT-INFO: basic block reordering modified layout of 4273 functions (35.89% of profiled, 2.01% of total)
> 
> BOLT-INFO: UCE removed 1 blocks and 4 bytes of code
> 
> BOLT-INFO: 68 Functions were reordered by LoopInversionPass
> 
> <unknown>:0: error: fixup value out of range
> 
> <unknown>:0: error: fixup value out of range
> 
> <unknown>:0: error: fixup value out of range
> 
> <unknown>:0: error: fixup value out of range
> 
> <unknown>:0: error: fixup value out of range
> 
> <unknown>:0: error: fixup value out of range
> 
> <unknown>:0: error: fixup value out of range
> 
> <unknown>:0: error: fixup value out of range
> 
> ```
> 
> 
> 
> More information on LTO-PGO-BOLT can be found on https://llvm.org/docs/AdvancedBuilds.html

This change was tested on a buildbot: https://lab.llvm.org/buildbot/#/builders/113/builds/2934

Can you please try cleaning the build directory?

https://github.com/llvm/llvm-project/pull/109351