We don't use any elliptic curves from OpenSSL anymore, nor include this
header anywhere but optionally in the tests of secp256k1 (which has
its own autoconf setup).
Reported by sinetek on IRC.
- guard PKG_PROG_PKG_CONFIG with an m4_ifdef. If not building for windows,
require it
- add nops as necessary in case the ifdef reduces the if/then to nothing
- AC_SUBST some missing _LIBS. These were split out over time, but not all were
properly substituted. They continued to work if pkg-config is installed
because it does the AC_SUBST itself
Disabling warnings can be tricky, because doing so can cause a different
compiler to create new warnings about unsupported disable flags. Also, some
warnings don't surface until they're paired with another warning (gcc). For
example, adding "-Wno-foo" won't cause any trouble, but if there's a legitimate
warning emitted, the "unknown option -Wno-foo" will show up as well.
Work around this in 2 ways:
1. When checking to see if -Wno-foo is supported, check for "-Wfoo" instead.
2. Enable -Werror while checking 1.
If "-Werror -Wfoo" compiles, "-Wno-foo" is almost guaranteed to be supported.
-Werror itself is also checked. If that fails to compile by itself, it likely
means that the user added a flag that adds a warning. In that case, -Werror
won't be used while checking, and the build may be extra noisy. The user would
need to fix the bad input flag.
Also, silence 2 more additional warnings that can show up post-c++11.
Unfortunately, the target namees defined at the Makefile.am level can't be used
for *.in substitution. So these new defines will have to stay synced up with
those targets.
Using the new variables for the deploy targets in the main Makefile.am will
ensure that they stay in sync, otherwise build tests will fail.
Move libsnark in-repo as a git subtree
This PR pulls in the libsnark subtree at the exact commit that we currently fetch via the depends system. To verify:
```
$ ./contrib/devtools/git-subtree-check.sh src/snark
src/snark in HEAD was last updated to upstream commit 9ada3f84ab484c57b2247c2f41091fd6a0916573 (tree c10a38c759)
src/snark in HEAD currently refers to tree 34e916d3f6
:100644 100644 427f4f4ce913e54da68b M Makefile
:040000 040000 42f29e42d1dd73536163 M src
FAIL: subtree directory tree doesn't match subtree commit tree
```
This shows that there are changes relative to what we currently use, due to the later commits in the PR. If we exclude them, we see that the code is identical:
```
$ git checkout 26a8f68ea8
$ ./contrib/devtools/git-subtree-check.sh src/snark
src/snark in HEAD was last updated to upstream commit 9ada3f84ab484c57b2247c2f41091fd6a0916573 (tree c10a38c759)
src/snark in HEAD currently refers to tree c10a38c759
GOOD
```
Closes#820.
