Refactor sym_upload in tools to extract code into common/linux, and minor fixes

src/common/linux/http_upload.cc

Index: src/common/linux/http_upload.cc
diff --git a/src/common/linux/http_upload.cc b/src/common/linux/http_upload.cc
index 4492fe84542c00b87cae9019c1959da776078812..702526af753779c450fdff184e15f35595ae7a4c 100644
--- a/src/common/linux/http_upload.cc
+++ b/src/common/linux/http_upload.cc
@@ -72,7 +72,9 @@ bool HTTPUpload::SendRequest(const string &url,
   // We may have been linked statically; if curl_easy_init is in the
   // current binary, no need to search for a dynamic version.
   void* curl_lib = dlopen(NULL, RTLD_NOW);
-  if (!curl_lib || dlsym(curl_lib, "curl_easy_init") == NULL) {
+  if (!CheckCurlLib(curl_lib)) {
+    fprintf(stderr,
+            "Failed to open curl lib from binary, use libcurl.so instead\n");
     dlerror();  // Clear dlerror before attempting to open libraries.
     dlclose(curl_lib);
     curl_lib = NULL;
@@ -113,6 +115,10 @@ bool HTTPUpload::SendRequest(const string &url,
   *(void**) (&curl_easy_setopt) = dlsym(curl_lib, "curl_easy_setopt");
   (*curl_easy_setopt)(curl, CURLOPT_URL, url.c_str());
   (*curl_easy_setopt)(curl, CURLOPT_USERAGENT, kUserAgent);
+  // Support multithread by disabling timeout handling, would get SIGSEGV with
+  // Curl_resolv_timeout in stack trace otherwise.
+  // See https://curl.haxx.se/libcurl/c/threadsafe.html
+  (*curl_easy_setopt)(curl, CURLOPT_NOSIGNAL, 1);
   // Set proxy information if necessary.
   if (!proxy.empty())
     (*curl_easy_setopt)(curl, CURLOPT_PROXY, proxy.c_str());
@@ -198,6 +204,13 @@ bool HTTPUpload::SendRequest(const string &url,
 }
 
 // static
+bool HTTPUpload::CheckCurlLib(void* curl_lib) {
+  return curl_lib &&
+      dlsym(curl_lib, "curl_easy_init") &&
+      dlsym(curl_lib, "curl_easy_setopt");
+}
+
+// static
 bool HTTPUpload::CheckParameters(const map<string, string> &parameters) {
   for (map<string, string>::const_iterator pos = parameters.begin();
        pos != parameters.end(); ++pos) {