Make use of constant time ecdsa_sign code in ecdsa_sign_recoverable #725

1. 
   jonasnick commented at 5:35 pm on March 23, 2020: contributor

   We can not add secp256k1_ecdsa_sign_recoverable to valgrind_ctime_tests (added in PR #708) because it is mostly a copy of the old ecdsa_sign function which was not constant time in edge cases. Instead of fixing sign_recoverable and again having duplicate code we should add an internal function with the code shared between the two functions (similar to https://github.com/bitcoin-core/secp256k1/commit/ab4fd520cc9f995fb1d2ffe825a2747671b9848d).

   Let’s get #701 in first because it also touches ecdsa_sign.

2. real-or-random added this to the milestone initial release (1.0.0-rc.1) on Apr 28, 2020
3. real-or-random closed this on Jun 8, 2020

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4. 
   elichai commented at 3:13 pm on June 8, 2020: contributor

   @jonasnick hehe I didn’t know this issue existed :)

Contributors
jonasnick elichai

Milestone
stable release (1.0.0-rc.1)