String.prototype.toLocaleUpperCase bug in tr_TR.UTF-8 Locale #10765

• Version: v7.2.0, v7.4.0
• Platform: Linux PCNAME 4.4.0-57-generic Mani #78-Ubuntu SMP Fri Dec 9 23:50:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
• Subsystem: core JS

In Turkish locale, String.prototype.toLocaleUpperCase does not behave correctly on the letter 'ç'. Specifically,

'Ç'.toLocaleLowerCase() === 'ç'
'ç'.toLocaleUpperCase() !== 'Ç'

This bug was not present in v6.9.2 :

'Ç'.toLocaleLowerCase() === 'ç'
'ç'.toLocaleUpperCase() === 'Ç'