Convert the rest of the codebase to C89.

Update build system to enforce -std=c89 -pedantic.

src/bench_recover.c

@@ -14,13 +14,15 @@ typedef struct {
 } bench_recover_t;
 
 void bench_recover(void* arg) {
+    int i;
     bench_recover_t *data = (bench_recover_t*)arg;
-
     unsigned char pubkey[33];
-    for (int i=0; i<20000; i++) {
+
+    for (i = 0; i < 20000; i++) {
+        int j;
         int pubkeylen = 33;
         CHECK(secp256k1_ecdsa_recover_compact(data->msg, data->sig, pubkey, &pubkeylen, 1, i % 2));
-        for (int j = 0; j < 32; j++) {
+        for (j = 0; j < 32; j++) {
             data->sig[j + 32] = data->msg[j];    /* Move former message to S. */
             data->msg[j] = data->sig[j];         /* Move former R to message. */
             data->sig[j] = pubkey[j + 1];        /* Move recovered pubkey X coordinate to R (which must be a valid X coordinate). */
@@ -29,16 +31,17 @@ void bench_recover(void* arg) {
 }
 
 void bench_recover_setup(void* arg) {
+    int i;
     bench_recover_t *data = (bench_recover_t*)arg;
 
-    for (int i = 0; i < 32; i++) data->msg[i] = 1 + i;
-    for (int i = 0; i < 64; i++) data->sig[i] = 65 + i;
+    for (i = 0; i < 32; i++) data->msg[i] = 1 + i;
+    for (i = 0; i < 64; i++) data->sig[i] = 65 + i;
 }
 
 int main(void) {
+    bench_recover_t data;
     secp256k1_start(SECP256K1_START_VERIFY);
 
-    bench_recover_t data;
     run_benchmark(bench_recover, bench_recover_setup, NULL, &data, 10, 20000);
 
     secp256k1_stop();