[CodeGen] prevent abnormal on invalid attributes

Currently, when an invalid attribute is encountered on processing a .s file,
clang will abort due to llvm_unreachable.  Invalid user input should not cause
an abnormal termination of the compiler.  Change the interface to return a
boolean to indicate the failure as a first step towards improving hanlding of
malformed user input to clang.

Signed-off-by: Saleem Abdulrasool <compnerd@compnerd.org>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@188047 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/lto/LTOModule.cpp b/tools/lto/LTOModule.cpp
index e89733f..1812346 100644
--- a/tools/lto/LTOModule.cpp
+++ b/tools/lto/LTOModule.cpp
@@ -738,9 +738,10 @@
       // FIXME: should we handle aliases?
       markDefined(*Symbol);
     }
-    virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) {
+    virtual bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) {
       if (Attribute == MCSA_Global)
         markGlobal(*Symbol);
+      return true;
     }
     virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
                               uint64_t Size , unsigned ByteAlignment) {