[llvm] [CMake] Remove HAVE_DLFCN_H and HAVE_DLADDR (PR #123879)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `ppc64-flang-aix` running on `ppc64-flang-aix-test` while building `llvm,utils` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/201/builds/1851

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

```
Step 5 (build-unified-tree) failure: build (failure)
...
44.830 [7858/10/153] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Memory.cpp.o
44.894 [7857/10/154] Building C object lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3.c.o
45.054 [7856/10/155] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/YAMLParser.cpp.o
45.114 [7855/10/156] Building C object lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3_dispatch.c.o
45.261 [7854/10/157] Building C object lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3_neon.c.o
45.382 [7853/10/158] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/RWMutex.cpp.o
45.632 [7852/10/159] Building C object lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3_portable.c.o
45.998 [7851/10/160] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Threading.cpp.o
46.245 [7850/10/161] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Process.cpp.o
46.704 [7849/10/162] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Signals.cpp.o
FAILED: lib/Support/CMakeFiles/LLVMSupport.dir/Signals.cpp.o 
/home/llvm/llvm-external-buildbots/clang.17.0.2/bin/clang++ -DGTEST_HAS_RTTI=0 -D_DEBUG -D_GLIBCXX_ASSERTIONS -D_LARGE_FILE_API -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/build/lib/Support -I/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/llvm/lib/Support -I/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/build/include -I/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/llvm/include -mcmodel=large -fPIC -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -ffunction-sections -fdata-sections  -O3 -DNDEBUG -std=c++17 -UNDEBUG  -fno-exceptions -funwind-tables -fno-rtti -MD -MT lib/Support/CMakeFiles/LLVMSupport.dir/Signals.cpp.o -MF lib/Support/CMakeFiles/LLVMSupport.dir/Signals.cpp.o.d -o lib/Support/CMakeFiles/LLVMSupport.dir/Signals.cpp.o -c /home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/llvm/lib/Support/Signals.cpp
In file included from /home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/llvm/lib/Support/Signals.cpp:277:
/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/llvm/lib/Support/Unix/Signals.inc:818:5: error: unknown type name 'Dl_info'
  818 |     Dl_info dlinfo;
      |     ^
/home/llvm/llvm-external-buildbots/workers/ppc64-flang-aix-test/ppc64-flang-aix-build/llvm-project/llvm/lib/Support/Unix/Signals.inc:833:5: error: unknown type name 'Dl_info'
  833 |     Dl_info dlinfo;
      |     ^
2 errors generated.
46.784 [7849/9/163] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Program.cpp.o
48.314 [7849/8/164] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/Path.cpp.o
48.463 [7849/7/165] Building CXX object lib/TableGen/CMakeFiles/LLVMTableGen.dir/Error.cpp.o
49.455 [7849/6/166] Building CXX object lib/TableGen/CMakeFiles/LLVMTableGen.dir/DetailedRecordsBackend.cpp.o
49.869 [7849/5/167] Building CXX object lib/TableGen/CMakeFiles/LLVMTableGen.dir/Parser.cpp.o
49.879 [7849/4/168] Building CXX object lib/Support/CMakeFiles/LLVMSupport.dir/VirtualFileSystem.cpp.o
50.166 [7849/3/169] Building CXX object lib/TableGen/CMakeFiles/LLVMTableGen.dir/JSONBackend.cpp.o
51.476 [7849/2/170] Building CXX object lib/TableGen/CMakeFiles/LLVMTableGen.dir/Main.cpp.o
59.112 [7849/1/171] Building CXX object lib/TableGen/CMakeFiles/LLVMTableGen.dir/Record.cpp.o
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/123879