add execvp

lib/emscripten/emtests/test_execvp.c

@@ -0,0 +1,17 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main() {
+    char command[] = "touch";
+    char arg1[] = "foo.txt";
+    char* argv[3];
+    argv[0] = command;
+    argv[1] = arg1;
+    argv[2] = 0;
+
+    printf("_execvp\n");
+    int result = execvp(command, argv);
+    // should not return, and not print this message
+    printf("error");
+    return 0;
+}