add missing va_end in execl* for correcness and static code analyzers

src/process/execl.c

@@ -16,6 +16,7 @@ int execl(const char *path, const char *argv0, ...)
 		for (i=1; i<argc; i++)
 			argv[i] = va_arg(ap, char *);
 		argv[i] = NULL;
+		va_end(ap);
 		return execv(path, argv);
 	}
 }

src/process/execle.c

@@ -17,6 +17,7 @@ int execle(const char *path, const char *argv0, ...)
 		for (i=1; i<=argc; i++)
 			argv[i] = va_arg(ap, char *);
 		envp = va_arg(ap, char **);
+		va_end(ap);
 		return execve(path, argv, envp);
 	}
 }

src/process/execlp.c

@@ -16,6 +16,7 @@ int execlp(const char *file, const char *argv0, ...)
 		for (i=1; i<argc; i++)
 			argv[i] = va_arg(ap, char *);
 		argv[i] = NULL;
+		va_end(ap);
 		return execvp(file, argv);
 	}
 }