[llvm] [NFC][PGO] Factor downscaling of branch weights out of `Instrumentation` into `ProfileData` (PR #153735)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `openmp-s390x-linux` running on `systemz-1` while building `llvm` at step 5 "compile-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/15080

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (compile-openmp) failure: build (failure)
...
12.687 [4980/4/473] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/StructuralHash.cpp.o
12.711 [4979/4/474] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Type.cpp.o
12.736 [4978/4/475] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/TypedPointerType.cpp.o
12.758 [4977/4/476] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/TypeFinder.cpp.o
12.780 [4976/4/477] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Use.cpp.o
12.822 [4975/4/478] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/User.cpp.o
12.848 [4974/4/479] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Value.cpp.o
12.874 [4973/4/480] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/ValueSymbolTable.cpp.o
12.896 [4972/4/481] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/VectorTypeUtils.cpp.o
14.246 [4971/4/482] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o
FAILED: lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o 
CCACHE_CPP2=yes CCACHE_HASHDIR=yes CCACHE_SLOPPINESS=pch_defines,time_macros /usr/bin/ccache /usr/bin/c++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/lib/IR -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/IR -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/include -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/include -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-uninitialized -Wno-nonnull -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wno-misleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -UNDEBUG -std=c++17 -MD -MT lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o -MF lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o.d -o lib/IR/CMakeFiles/LLVMCore.dir/ProfDataUtils.cpp.o -c /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/IR/ProfDataUtils.cpp
/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/IR/ProfDataUtils.cpp: In function 'llvm::SmallVector<unsigned int> llvm::downscaleWeights(llvm::ArrayRef<long unsigned int>, std::optional<long unsigned int>)':
/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/lib/IR/ProfDataUtils.cpp:282:10: error: could not convert 'DownscaledWeights' from 'SmallVector<[...],4>' to 'SmallVector<[...],12>'
  282 |   return DownscaledWeights;
      |          ^~~~~~~~~~~~~~~~~
      |          |
      |          SmallVector<[...],4>
15.280 [4971/3/483] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Instructions.cpp.o
24.045 [4971/2/484] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Metadata.cpp.o
25.334 [4971/1/485] Building CXX object lib/IR/CMakeFiles/LLVMCore.dir/Verifier.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/153735