unwind: rename `__personality_routine` to `_Unwind_Personality_Fn`

This patch renames `__personality_routine` to `_Unwind_Personality_Fn`
in `unwind.h`. Both `unwind.h` from clang and GCC headers use this name
instead of `__personality_routine`. With this patch one is also able to
build libc++abi with libunwind support on Windows.

Patch by Markus Böck!

Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 14798b44658c8b30b44afae20d0f391e88eb5bec
diff --git a/src/UnwindLevel1-gcc-ext.c b/src/UnwindLevel1-gcc-ext.c
index 008df81..310b836 100644
--- a/src/UnwindLevel1-gcc-ext.c
+++ b/src/UnwindLevel1-gcc-ext.c
@@ -149,7 +149,7 @@
 
     struct _Unwind_Context *context = (struct _Unwind_Context *)&cursor;
     // Get and call the personality function to unwind the frame.
-    __personality_routine handler = (__personality_routine) frameInfo.handler;
+    _Unwind_Personality_Fn handler = (_Unwind_Personality_Fn)frameInfo.handler;
     if (handler == NULL) {
       return _URC_END_OF_STACK;
     }