[llvm] Xtensa] Implement windowed call ABI. (PR #130001)

[Matt Arsenault via llvm-commits]

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@@ -23,9 +23,15 @@
 
 using namespace llvm;
 
+/* minimum frame = reg save area (4 words) plus static chain (1 word)
+   and the total number of words must be a multiple of 128 bits.  */
+/* Width of a word, in units (bytes).  */
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arsenm wrote:

 C++ style comments 

https://github.com/llvm/llvm-project/pull/130001