[Xtensa] Correct visibility of the Xtensa backend initialize functions.

Make backend initialize functions public and visible outside library.

Closes llvm#31

Author: andreisfr

llvm/lib/Target/Xtensa/AsmParser/XtensaAsmParser.cpp

@@ -1074,6 +1074,6 @@ bool XtensaAsmParser::checkRegister(unsigned RegNo) {
 }
 
 // Force static initialization.
-extern "C" void LLVMInitializeXtensaAsmParser() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeXtensaAsmParser() {
   RegisterMCAsmParser<XtensaAsmParser> X(TheXtensaTarget);
 }

llvm/lib/Target/Xtensa/MCTargetDesc/XtensaMCTargetDesc.cpp

@@ -78,7 +78,7 @@ createXtensaObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
   return new XtensaTargetELFStreamer(S);
 }
 
-extern "C" void LLVMInitializeXtensaTargetMC() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeXtensaTargetMC() {
   // Register the MCAsmInfo.
   TargetRegistry::RegisterMCAsmInfo(TheXtensaTarget, createXtensaMCAsmInfo);
 

llvm/lib/Target/Xtensa/TargetInfo/XtensaTargetInfo.cpp

@@ -14,7 +14,7 @@ using namespace llvm;
 namespace llvm {
 Target TheXtensaTarget;
 }
-extern "C" void LLVMInitializeXtensaTargetInfo() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeXtensaTargetInfo() {
   RegisterTarget<Triple::xtensa> X(TheXtensaTarget, "xtensa", "Xtensa 32",
                                    "XTENSA");
 }

llvm/lib/Target/Xtensa/XtensaAsmPrinter.cpp

@@ -271,6 +271,6 @@ void XtensaAsmPrinter::printMemOperand(const MachineInstr *MI, int opNum,
 }
 
 // Force static initialization.
-extern "C" void LLVMInitializeXtensaAsmPrinter() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeXtensaAsmPrinter() {
   RegisterAsmPrinter<XtensaAsmPrinter> A(TheXtensaTarget);
 }

llvm/lib/Target/Xtensa/XtensaTargetMachine.cpp

@@ -23,7 +23,7 @@
 
 using namespace llvm;
 
-extern "C" void LLVMInitializeXtensaTarget() {
+extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeXtensaTarget() {
   // Register the target.
   RegisterTargetMachine<XtensaTargetMachine> A(TheXtensaTarget);
 }