Build failure with Clang 14+ due to function warning attribute

After JDK-8214976, OpenJDK cannot build with Clang 14 or newer. This is because Clang 14+ currently does not support merging warning attributes of functions. Build failure looks like:
```
jdkGitHead/src/hotspot/share/utilities/globalDefinitions.hpp:165:1: error: 'warning' attribute does not appear on the first declaration
FORBID_C_FUNCTION(void exit(int), "use os::exit");
^
jdkGitHead/src/hotspot/share/utilities/compilerWarnings_gcc.hpp:85:29: note: expanded from macro 'FORBID_C_FUNCTION'
  extern "C" __attribute__((__warning__(alternative))) signature;
                            ^
/usr/include/stdlib.h:617:13: note: previous declaration is here
extern void exit (int __status) __THROW __attribute__ ((__noreturn__));
```

https://github.com/llvm/llvm-project/issues/56519 has been opened and will be fixed in a future Clang release. I propose we temporarily disable the warning attribute when building with Clang, until the LLVM issue #56519 is fixed and released.