Allow expressions in MEMORY command.

Previously, we allowed only integers in this context. Now you can
write expressions there. LLD is now able to handle the following
linker, for example.

  MEMORY { rom (rx) : ORIGIN = (1024 * 1024) }

llvm-svn: 300131

lld/ELF/ScriptParser.cpp

@@ -1102,12 +1102,7 @@ uint64_t ScriptParser::readMemoryAssignment(StringRef S1, StringRef S2,
     return 0;
   }
   expect("=");
-
-  // TODO: Fully support constant expressions.
-  if (Optional<uint64_t> Val = parseInt(next()))
-    return *Val;
-  setError("nonconstant expression for " + S1);
-  return 0;
+  return readExpr()().getValue();
 }
 
 // Parse the MEMORY command as specified in: