Add dlwrap.c to binutils to simulate dlopen/dlsym for gold plugin

dlwrap/dlwrap.c

+#include <stdio.h>
+#include <string.h>
+
+/* This is a libdl emulation library which provides the statically-linked LLVM
+ * gold plugin as if it were dynamically loaded.
+ *
+ * The only supported usage is the following:
+ *
+ *   void *plugin = dlopen("LLVMgold", RTLD_NOW);
+ *   void *onload_function = dlsym(plugin, "onload");
+ */
+
+
+/* This must match RTLD_NOW in dlwrap.h */
+#define RTLD_NOW   0x2
+
+static int dummy;
+static int haserr = 0;
+static char errmsg[200];
+
+/* This is not the real signature of this function,
+ * but we just need the symbol address.
+ */
+void llvm_plugin_onload();
+
+void *pnacl_dlopen(const char *filename, int flag) {
+  void *ret;
+  if (flag != 0 && flag != RTLD_NOW) {
+    sprintf(errmsg, "Error: Unknown flag to pnacl_dlopen: %d\n", flag);
+    haserr = 1;
+    return NULL;
+  }
+  if (strstr(filename, "LLVMgold") == NULL) {
+    sprintf(errmsg, "Error: Unexpected pnacl_dlopen: %s\n", filename);
+    haserr = 1;
+    return NULL;
+  }
+  return (void*)&dummy;
+}
+
+char *pnacl_dlerror(void) {
+  if (haserr) {
+    haserr = 0;
+    return errmsg;
+  }
+  return NULL;
+}
+
+void *pnacl_dlsym(void *handle, const char *symbol) {
+  if (handle != (void*)&dummy) {
+    sprintf(errmsg, "Error: Unexpected pnacl_dlsym handle\n");
+    haserr = 1;
+    return NULL;
+  }
+
+  if (strcmp(symbol, "onload") != 0) {
+    sprintf(errmsg, "Error: Unexpected pnacl_dlsym symbol: %s\n", symbol);
+    haserr = 1;
+    return NULL;
+  }
+  return (void*)&llvm_plugin_onload;
+}
+
+int pnacl_dlclose(void *handle) {
+  return 0;
+}