add the syscall and create a test

lib/emscripten/emtests/test_getcwd.c

@@ -0,0 +1,10 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main() {
+    const unsigned int size = 256;
+    char cwd[size] = {};
+    char* buf = getcwd(cwd, size);
+    printf("getcwd\n");
+    return 0;
+}

lib/emscripten/emtests/test_getcwd.out

@@ -0,0 +1 @@
+getcwd