Fix use of execvp, earlier fix was short sighted and only worked

when godot could be found in PATH.
The correct fix is to use sysctl to get the path to the current executable
this also fixes the ability to call external commands.

drivers/unix/os_unix.cpp

@@ -53,6 +53,7 @@
 
 #if defined(__FreeBSD__) || defined(__OpenBSD__)
 #include <sys/param.h>
+#include <sys/sysctl.h>
 #endif
 #include "project_settings.h"
 #include <assert.h>
@@ -298,17 +299,7 @@ Error OS_Unix::execute(const String &p_path, const List<String> &p_arguments, bo
 			args.push_back((char *)cs[i].get_data()); // shitty C cast
 		args.push_back(0);
 
-#ifdef __FreeBSD__
-		if (p_path.find("/") != -1) {
-			// exec name contains path so use it
-			execv(p_path.utf8().get_data(), &args[0]);
-		} else {
-			// use program name and search through PATH to find it
-			execvp(getprogname(), &args[0]);
-		}
-#else
 		execvp(p_path.utf8().get_data(), &args[0]);
-#endif
 		// still alive? something failed..
 		fprintf(stderr, "**ERROR** OS_Unix::execute - Could not create child process while executing: %s\n", p_path.utf8().get_data());
 		abort();
@@ -462,12 +453,23 @@ String OS_Unix::get_executable_path() const {
 		return OS::get_executable_path();
 	}
 	return b;
-#elif defined(__FreeBSD__) || defined(__OpenBSD__)
+#elif defined(__OpenBSD__)
 	char resolved_path[MAXPATHLEN];
 
 	realpath(OS::get_executable_path().utf8().get_data(), resolved_path);
 
 	return String(resolved_path);
+#elif defined(__FreeBSD__)
+	int mib[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PATHNAME, -1 };
+	char buf[MAXPATHLEN];
+	size_t len = sizeof(buf);
+	if (sysctl(mib, 4, buf, &len, NULL, 0) != 0) {
+		WARN_PRINT("Couldn't get executable path from sysctl");
+		return OS::get_executable_path();
+	}
+	String b;
+	b.parse_utf8(buf);
+	return b;
 #elif defined(__APPLE__)
 	char temp_path[1];
 	uint32_t buff_size = 1;