[Bug target/85683] [8 Regression] GCC 8 stopped using RMW (Read Modify Write) instructions on x86[_64]

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85683
Bug 85683 depends on bug 85756, which changed state.

Bug 85756 Summary: [9 regression] wrong code at -Os on x86-64-linux-gnu in 
32-bit mode
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85756

           What    |Removed                     |Added
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             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED