Merge bitcoin-core/secp256k1#988: Make signing table fully static

7dfceceea6 build: Remove #undef hack for ASM in the precomputation programs (Tim Ruffing)
bb36fe9be0 ci: Test `make precomp` (Tim Ruffing)
d94a37a20c build: Remove CC_FOR_BUILD stuff (Tim Ruffing)
ad63bb4c29 build: Prebuild and distribute ecmult_gen table (Tim Ruffing)
ac49361ed0 prealloc: Get rid of manual memory management for prealloc contexts (Tim Ruffing)
6573c08f65 ecmult_gen: Tidy precomputed file and save space (Tim Ruffing)
5eba83f17c ecmult_gen: Precompute tables for all values of ECMULT_GEN_PREC_BITS (Tim Ruffing)
fdb33dd122 refactor: Make PREC_BITS a parameter of ecmult_gen_build_prec_table (Tim Ruffing)
a4875e30a6 refactor: Move default callbacks to util.h (Tim Ruffing)
4c94c55bce doc: Remove obsolete hint for valgrind stack size (Tim Ruffing)
5106226991 exhaustive_tests: Fix with ecmult_gen table with custom generator (Tim Ruffing)
e1a76530db refactor: Make generator a parameter of ecmult_gen_create_prec_table (Tim Ruffing)
9ad09f6911 refactor: Rename program that generates static ecmult_gen table (Tim Ruffing)
8ae18f1ab3 refactor: Rename file that contains static ecmult_gen table (Tim Ruffing)
00d2fa116e ecmult_gen: Make code consistent with comment (Tim Ruffing)
3b0c2185ea ecmult_gen: Simplify ecmult_gen context after making table static (Tim Ruffing)
e43ba02cfc refactor: Decouple table generation and ecmult_gen context (Tim Ruffing)
22dc2c0a0d ecmult_gen: Move table creation to new file and force static prec (Tim Ruffing)

Pull request description:

  This resolves #893,  resolves #692 (and also resolves bitcoin/bitcoin#22854).

  - [x] Extract table generation to separate function in separate file (to be used by generation script and exhaustive tests)
  - [x] Tidy up
    - [x] Remove code that deals with non-static tables
    - [x] Make functions that need ecmult_gen not depend on signing context
    - [x] Rename stuff to make it fit the new structure and consistent with how we hande verification tables (#956)
  - [x] Fix exhaustive tests
    - [x] Make table generation function take generator as input
    - [x] Overwrite the static tables with a table with custom generator in exhaustive tests
  - [x] Overhaul script that generates table files
    - [x] Make table generation function take PREC_BITS as input (I have some code already, just not yet in this branch)
    - [x] Change generation script to generate three tables (for all three values of ECMULT_GEN_PREC_BITS)
  - [x] Ship pre-built tables
    - [x] Add pregenerated table file to repo
    - [x] Remove generation of table file from build process (like in #956)
    - [x] Remove left-over stuff (e.g., detecting a compiler running on the build machine) from build system
  - [x] Final cleanups (copyright headers, commit, messages, etc.)
  - [ ] (separate PR:) Make sure link-time optimization remove corresponding static tables (and code) when no signing/verifcation function is called
  - [ ] (separate PR:) Compile precomputation as a separate object file and link it (https://github.com/bitcoin-core/secp256k1/pull/988#issuecomment-977813538)
  - [ ] (separate PR:) Document the backwards-compatible API changes made in this PR and in #956.
    - [ ] Maybe deprecate the static context

ACKs for top commit:
  sipa:
    ACK 7dfceceea6
  robot-dreams:
    ACK 7dfceceea6 (based on range-diff between 56284c7d44c0ed46e636588bfbf6c403b7dfa6c1 and 7dfceceea6)

Tree-SHA512: 6efb3f36f05efe3b79bbd877881fe1409f71fd6488d24c811b2e77d9f053bed78670dd1dcbb42ad780458a51c4ffa36de9cd6567271b22041dc7a122ceb677c5

ci/cirrus.sh

@@ -48,7 +48,19 @@ then
         $EXEC ./bench
     } >> bench.log 2>&1
 fi
+
 if [ "$CTIMETEST" = "yes" ]
 then
     ./libtool --mode=execute valgrind --error-exitcode=42 ./valgrind_ctime_test > valgrind_ctime_test.log 2>&1
 fi
+
+# Rebuild precomputed files (if not cross-compiling).
+if [ -z "$HOST" ]
+then
+    make clean-precomp
+    make precomp
+fi
+
+# Check that no repo files have been modified by the build.
+# (This fails for example if the precomp files need to be updated in the repo.)
+git diff --exit-code