libunwind: Introduce __libunwind_config.h.

Introduce __libunwind_config.h to avoid cross repository circular
dependency with libcxxabi.

llvm-svn: 242642
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 5191fe9509fab84b7681c7ef6f4eceef877d5339
diff --git a/src/UnwindLevel1.c b/src/UnwindLevel1.c
index 61abd89..caef0cf 100644
--- a/src/UnwindLevel1.c
+++ b/src/UnwindLevel1.c
@@ -23,7 +23,7 @@
 #include "unwind.h"
 #include "config.h"
 
-#if !LIBCXXABI_ARM_EHABI
+#if !_LIBUNWIND_ARM_EHABI
 
 static _Unwind_Reason_Code
 unwind_phase1(unw_context_t *uc, _Unwind_Exception *exception_object) {
@@ -530,5 +530,5 @@
   _Unwind_SetGR(context, 15, value | thumb_bit);
 }
 
-#endif // !LIBCXXABI_ARM_EHABI
+#endif // !_LIBUNWIND_ARM_EHABI