[libc++/abi/unwind] Rename Lit features for no exceptions to 'no-exceptions'

Instead of having different names for the same Lit feature accross code
bases, use the same name everywhere. This NFC commit is in preparation
for a refactor where all three projects will be using the same Lit
feature detection logic, and hence it won't be convenient to use
different names for the feature.

Differential Revision: https://reviews.llvm.org/D78370
diff --git a/libcxxabi/test/cxa_vec_new_overflow_PR41395.pass.cpp b/libcxxabi/test/cxa_vec_new_overflow_PR41395.pass.cpp
index 67b060e..84ba978 100644
--- a/libcxxabi/test/cxa_vec_new_overflow_PR41395.pass.cpp
+++ b/libcxxabi/test/cxa_vec_new_overflow_PR41395.pass.cpp
@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-// UNSUPPORTED: libcxxabi-no-exceptions
+// UNSUPPORTED: no-exceptions
 
 #include "cxxabi.h"
 #include <new>