[ELF] - Linkerscript - fix handling of OUTPUT_ARCH command.

OUTPUT_ARCH command can contain architecture values separated with ":", like:
OUTPUT_ARCH(i386:x86-64)

We did not support that, because got 3 lexer tokens here after recent changes.

This trivial patch fixes the issue, now whole expression inside 
OUTPUT_ARCH is just ignored.

Differential revision: https://reviews.llvm.org/D29640

llvm-svn: 294432
diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index c6b9009..2fa2ff4 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -1247,10 +1247,10 @@
 }
 
 void ScriptParser::readOutputArch() {
-  // Error checking only for now.
+  // OUTPUT_ARCH is ignored for now.
   expect("(");
-  skip();
-  expect(")");
+  while (!Error && !consume(")"))
+    skip();
 }
 
 void ScriptParser::readOutputFormat() {