Merge #663: Patch out any instances of printf in upstream

7a0c60e secp256k1-sys: patch out checked_malloc (Andrew Poelstra)
942a0e5 build.rs: patch out any calls to `printf` (Andrew Poelstra)
51dab7a vendor-libsecp: remove util.h patch (Andrew Poelstra)

Pull request description:

  Rather than using a new patchfile, just `#define` it away. Also includes a commit which removes one of the existing patchfiles, which I discovered was out of date while auditing the others to see if they could be replaced by `#define`s. (No, they cannot.)

  Fixes #660

ACKs for top commit:
  tcharding:
    AFAICT this is right to go, ACK 7a0c60e
  Kixunil:
    ACK 7a0c60e

Tree-SHA512: 83ba70b000919fb8a929804c9d5929a9929b80515f0594925d3789ef896889d3c909f9fa920bac45470611607b84f509723544fa442ff1a51eefba0de75bf68f

secp256k1-sys/build.rs

@@ -20,11 +20,16 @@ fn main() {
                .include("depend/secp256k1/include")
                .include("depend/secp256k1/src")
                .flag_if_supported("-Wno-unused-function") // some ecmult stuff is defined but not used upstream
+               .flag_if_supported("-Wno-unused-parameter") // patching out printf causes this warning
                .define("SECP256K1_API", Some(""))
                .define("ENABLE_MODULE_ECDH", Some("1"))
                .define("ENABLE_MODULE_SCHNORRSIG", Some("1"))
                .define("ENABLE_MODULE_EXTRAKEYS", Some("1"))
-               .define("ENABLE_MODULE_ELLSWIFT", Some("1"));
+               .define("ENABLE_MODULE_ELLSWIFT", Some("1"))
+               // upstream sometimes introduces calls to printf, which we cannot compile
+               // with WASM due to its lack of libc. printf is never necessary and we can
+               // just #define it away.
+               .define("printf(...)", Some(""));
 
     if cfg!(feature = "lowmemory") {
         base_config.define("ECMULT_WINDOW_SIZE", Some("4")); // A low-enough value to consume negligible memory

secp256k1-sys/depend/secp256k1/src/util.h

@@ -8,9 +8,7 @@
 #define SECP256K1_UTIL_H
 
 #include "../include/secp256k1.h"
-extern int rustsecp256k1_v0_9_0_ecdsa_signature_parse_compact(
-        const rustsecp256k1_v0_9_0_context *ctx,
-        rustsecp256k1_v0_9_0_ecdsa_signature *sig, const unsigned char *input64);
+
 #include <stdlib.h>
 #include <stdint.h>
 #include <stdio.h>
@@ -147,11 +145,9 @@ static const rustsecp256k1_v0_9_0_callback default_error_callback = {
 #endif
 
 static SECP256K1_INLINE void *checked_malloc(const rustsecp256k1_v0_9_0_callback* cb, size_t size) {
-    void *ret = malloc(size);
-    if (ret == NULL) {
-        rustsecp256k1_v0_9_0_callback_call(cb, "Out of memory");
-    }
-    return ret;
+    (void) cb;
+    (void) size;
+    return NULL;
 }
 
 #if defined(__BIGGEST_ALIGNMENT__)

secp256k1-sys/depend/util.h.patch

@@ -1,6 +1,10 @@
-10c10,12
-< 
+148,152c148,150
+<     void *ret = malloc(size);
+<     if (ret == NULL) {
+<         secp256k1_callback_call(cb, "Out of memory");
+<     }
+<     return ret;
 ---
-> extern int secp256k1_ecdsa_signature_parse_compact(
->         const secp256k1_context *ctx,
->         secp256k1_ecdsa_signature *sig, const unsigned char *input64);
+>     (void) cb;
+>     (void) size;
+>     return NULL;