[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/catch_member_function_pointer_01.pass.cpp b/libcxxabi/test/catch_member_function_pointer_01.pass.cpp
index 3dc21df..f1d4e8d 100644
--- a/libcxxabi/test/catch_member_function_pointer_01.pass.cpp
+++ b/libcxxabi/test/catch_member_function_pointer_01.pass.cpp
@@ -9,7 +9,7 @@
 // GCC incorrectly allows PMF type "void (T::*)()" to be caught as "void (T::*)() const"
 // See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69375
 // XFAIL: gcc
-// UNSUPPORTED: libcxxabi-no-exceptions
+// UNSUPPORTED: no-exceptions
 #include <cassert>
 
 struct A