Rename libsecp256k1 to avoid collision with versions from ports

Index: modcargo-crates/secp256k1-sys-0.8.1/build.rs
--- modcargo-crates/secp256k1-sys-0.8.1/build.rs.orig
+++ modcargo-crates/secp256k1-sys-0.8.1/build.rs
@@ -60,7 +60,7 @@ fn main() {
                .file("depend/secp256k1/src/precomputed_ecmult.c")
                .file("depend/secp256k1/src/secp256k1.c");
 
-    if base_config.try_compile("libsecp256k1.a").is_err() {
+    if base_config.try_compile("libsecp256k1-rust.a").is_err() {
         // Some embedded platforms may not have, eg, string.h available, so if the build fails
         // simply try again with the wasm sysroot (but without the wasm type sizes) in the hopes
         // that it works.
