Merge bitcoin-core/secp256k1#1535: build: Replace hardcoded "auto" value with default one

4d9645bee0 cmake: Remove "AUTO" value of `SECP256K1_ECMULT_GEN_KB` option (Hennadii Stepanov)
a06805ee74 cmake: Remove "AUTO" value of `SECP256K1_ECMULT_WINDOW_SIZE` option (Hennadii Stepanov)
26b94ee92a autotools: Remove "auto" value of `--with-ecmult-gen-kb` option (Hennadii Stepanov)
122dbaeb37 autotools: Remove "auto" value of `--with-ecmult-window` option (Hennadii Stepanov)

Pull request description:

  "auto" implies that a value is being chosen based on build system introspection or host system capabilities. However, for the `--with-ecmult-window` and `--with-ecmult-gen-kb` options, the values "auto" are hardcoded, which might lead to confusion.

  This PR replaces "auto" with more appropriate default values.

  If Concept ACKed, I'll add equivalent commits for CMake.

ACKs for top commit:
  sipa:
    utACK 4d9645bee0
  real-or-random:
    utACK 4d9645bee0 good from my side, but let's see if we can get more (Concept) ACKs

Tree-SHA512: 9e68f73682c5310c68d2337594f13b99a52bfc365564e39df2e412b576635c90cccd2298406a4281f014916c4a1710e19c7390f05a4b0acbd09869bfb56f36ac

.github/workflows/ci.yml

@@ -21,8 +21,8 @@ env:
   MAKEFLAGS: '-j4'
   BUILD: 'check'
   ### secp256k1 config
-  ECMULTWINDOW: 'auto'
-  ECMULTGENKB: 'auto'
+  ECMULTWINDOW: 15
+  ECMULTGENKB: 22
   ASM: 'no'
   WIDEMUL: 'auto'
   WITH_VALGRIND: 'yes'