[libc] add remarks to the setjmp implementation

Author: SchrodingerZhu

libc/src/setjmp/x86_64/setjmp.cpp

@@ -6,6 +6,12 @@
 //
 //===----------------------------------------------------------------------===//
 
+// We use naked functions to avoid compiler-generated prologue and epilogue.
+// Despite GCC document list this as an supported case for extended asm, the 
+// generated code is not wrong as we only pass in constant operands to 
+// extended asm.
+// See https://github.com/llvm/llvm-project/issues/137055 for related remarks.
+
 #include "hdr/offsetof_macros.h"
 #include "src/__support/common.h"
 #include "src/__support/macros/config.h"