[lldb][test] Skip TestCppFloatingTypesSpecialization.py on older compilers
Fails with:
```
08:19:28 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/clang_1501_build/bin/clang++ -std=c++11 -g -O0 -isysroot "/Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.2.sdk" -arch arm64 -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/packages/Python/lldbsuite/test/make/../../../../..//include -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/lldb-build/tools/lldb/include -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/test/API/lang/cpp/floating-types-specialization -I/Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/packages/Python/lldbsuite/test/make -include /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/packages/Python/lldbsuite/test/make/test_common.h -fno-limit-debug-info -nostdlib++ -nostdinc++ -cxx-isystem /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/clang_1501_build/include/c++/v1/ --driver-mode=g++ -MT main.o -MD -MP -MF main.d -c -o main.o /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/test/API/lang/cpp/floating-types-specialization/main.cpp
08:19:28 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/test/API/lang/cpp/floating-types-specialization/main.cpp:3:24: error: __bf16 is not supported on this target
08:19:28 template <> struct Foo<__bf16> {};
08:19:28 ^
08:19:28 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/test/API/lang/cpp/floating-types-specialization/main.cpp:5:40: error: __bf16 is not supported on this target
08:19:28 template <> struct Foo<_Float16> : Foo<__bf16> {};
08:19:28 ^
08:19:28 /Users/ec2-user/jenkins/workspace/llvm.org/lldb-cmake-matrix/llvm-project/lldb/test/API/lang/cpp/floating-types-specialization/main.cpp:8:7: error: __bf16 is not supported on this target
08:19:28 Foo<__bf16> f0;
08:19:28 ^
08:19:28 3 errors generated.
08:19:28 make: *** [main.o] Error 1
```
On our Clang-15.0 CI.