src: readlink("/proc/self/exe") -> uv_exename()

This commit also adds error handling. A THP-enabled build terminated
with an out-of-memory error on a system without /proc because it cast
the -1 from readlink() to size_t (i.e. ULONG_MAX) and then tried to
allocate a string of that size.

PR-URL: #28333
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

src/large_pages/node_large_page.cc

@@ -115,8 +115,12 @@ static struct text_region FindNodeTextRegion() {
   std::string exename;
   {
       char selfexe[PATH_MAX];
-      ssize_t count = readlink("/proc/self/exe", selfexe, PATH_MAX);
-      exename = std::string(selfexe, count);
+
+      size_t size = sizeof(selfexe);
+      if (uv_exepath(selfexe, &size))
+        return nregion;
+
+      exename = std::string(selfexe, size);
   }
 
   while (std::getline(ifs, map_line)) {