Use empty() instead of size().

`!V.size()` where V is a vector is equivalent to `V.empty()`.

llvm-svn: 299501
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index ae72534..6e6e2d2 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -621,7 +621,7 @@
   // searched for in the region map. If the region map is empty, just
   // return. Note that this check doesn't happen at the very beginning
   // so that uses of undeclared regions can be caught.
-  if (!Opt.MemoryRegions.size())
+  if (Opt.MemoryRegions.empty())
     return nullptr;
 
   // See if a region can be found by matching section flags.