bench: Update help functions in bench and bench_internal

In the bench and bench_internal help functions argv was not being
passed, in this change we pass in argv[0] and use it in the help text.

Additionally instead of passing all of argv in bench_ecmult we now
just pass argv[0] and is used as the executable_path variable.

src/bench.c

@@ -12,7 +12,7 @@
 #include "util.h"
 #include "bench.h"
 
-static void help(int default_iters) {
+static void help(const char *executable_path, int default_iters) {
     printf("Benchmarks the following algorithms:\n");
     printf("    - ECDSA signing/verification\n");
 
@@ -36,7 +36,7 @@ static void help(int default_iters) {
     printf("The default number of iterations for each benchmark is %d. This can be\n", default_iters);
     printf("customized using the SECP256K1_BENCH_ITERS environment variable.\n");
     printf("\n");
-    printf("Usage: ./bench [args]\n");
+    printf("Usage: %s [args]\n", executable_path);
     printf("By default, all benchmarks will be run.\n");
     printf("args:\n");
     printf("    help              : display this help and exit\n");
@@ -189,7 +189,7 @@ int main(int argc, char** argv) {
     int default_iters = 20000;
     int iters = get_iters(default_iters);
     if (iters == 0) {
-        help(default_iters);
+        help(argv[0], default_iters);
         return EXIT_FAILURE;
     }
 
@@ -197,11 +197,11 @@ int main(int argc, char** argv) {
         if (have_flag(argc, argv, "-h")
            || have_flag(argc, argv, "--help")
            || have_flag(argc, argv, "help")) {
-            help(default_iters);
+            help(argv[0], default_iters);
             return EXIT_SUCCESS;
         } else if (invalid_args) {
             fprintf(stderr, "./bench: unrecognized argument.\n\n");
-            help(default_iters);
+            help(argv[0], default_iters);
             return EXIT_FAILURE;
         }
     }