[Bazel] Update for 957334382c

[GMNGeoffrey]

Summary

Update LLVM configuration to define HAVE_UNW_ADD_DYNAMIC_FDE for macOS
since https://github.com/llvm/llvm-project/commit/957334382c moved that
to a define.

[GMNGeoffrey]

Add comment to hardcoded config.h

utils/bazel/llvm-project-overlay/llvm/config.bzl

linux_defines = posix_defines + [
     "HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC=1",
 ]
 
 macos_defines = posix_defines + [
     "HAVE_MACH_MACH_H=1",
     "HAVE_MALLOC_MALLOC_H=1",
     "HAVE_MALLOC_ZONE_STATISTICS=1",
     "HAVE_PROC_PID_RUSAGE=1",
+    "HAVE_UNW_ADD_DYNAMIC_FDE=1",
 ]
 
 win32_defines = [
     # MSVC specific
     "stricmp=_stricmp",
     "strdup=_strdup",
 
     # LLVM features

utils/bazel/llvm-project-overlay/llvm/include/llvm/Config/config.h

 /* #undef HAVE_DLADDR */
 
 /* Define to 1 if we can register EH frames on this platform. */
 #define HAVE_REGISTER_FRAME 1
 
 /* Define to 1 if we can deregister EH frames on this platform. */
 #define HAVE_DEREGISTER_FRAME 1
 
+/* Define if __unw_add_dynamic_fde() is available on this platform. */
+/* HAVE_UNW_ADD_DYNAMIC_FDE defined in Bazel */
+
 /* Define to 1 if you have the <errno.h> header file. */
 #define HAVE_ERRNO_H 1
 
 /* Define to 1 if you have the <fcntl.h> header file. */
 #define HAVE_FCNTL_H 1
 
 /* Define to 1 if you have the <fenv.h> header file. */
 #define HAVE_FENV_H 1

utils/bazel/llvm_configs/config.h.cmake

 #cmakedefine HAVE_DLADDR ${HAVE_DLADDR}
 
 /* Define to 1 if we can register EH frames on this platform. */
 #cmakedefine HAVE_REGISTER_FRAME ${HAVE_REGISTER_FRAME}
 
 /* Define to 1 if we can deregister EH frames on this platform. */
 #cmakedefine HAVE_DEREGISTER_FRAME ${HAVE_DEREGISTER_FRAME}
 
+/* Define if __unw_add_dynamic_fde() is available on this platform. */
+#cmakedefine HAVE_UNW_ADD_DYNAMIC_FDE ${HAVE_UNW_ADD_DYNAMIC_FDE}
+
 /* Define to 1 if you have the <errno.h> header file. */
 #cmakedefine HAVE_ERRNO_H ${HAVE_ERRNO_H}
 
 /* Define to 1 if you have the <fcntl.h> header file. */
 #cmakedefine HAVE_FCNTL_H ${HAVE_FCNTL_H}
 
 /* Define to 1 if you have the <fenv.h> header file. */
 #cmakedefine HAVE_FENV_H ${HAVE_FENV_H}