Patch the ring build script to enable builds from source code

Turns out that ring includes pre-generated objects in cargo releases. It uses logic in its build scripts to determine whether the build is from a version published on cargo, or from source code. This logic is somewhat naively implemented by checking for the absence of a `.git` directory. This check falesly leads ring to believe it is building from a version published on crates.io, and fails when it tries to include the pregenerated files not present in the source code. To build from source code we must patch this flag.

Author: Juliette Pretot

third_party/ring/build.rs

@@ -330,7 +330,7 @@ fn ring_build_rs_main() {
     // If `.git` doesn't exist then assume that this is a packaged build where
     // we want to optimize for minimizing the build tools required: No Perl,
     // no nasm, etc.
-    let use_pregenerated = !is_git;
+    let use_pregenerated = false;
 
     // During local development, force warnings in non-Rust code to be treated
     // as errors. Since warnings are highly compiler-dependent and compilers