Fix linker option for -fprofile-arcs -ftest-coverage

Summary:
Linux toolchain accidentally added "-u__llvm_runtime_variable" when "-fprofile-arcs -ftest-coverage", this is not added when "--coverage" option is used.
Using "-u__llvm_runtime_variable" generates an empty default.profraw file while an application built with  "-fprofile-arcs -ftest-coverage" is running. 

Reviewers: calixte, marco-c, sylvestre.ledru

Reviewed By: marco-c

Subscribers: vsk, cfe-commits

Differential Revision: https://reviews.llvm.org/D54195

llvm-svn: 347677
diff --git a/clang/lib/Driver/ToolChains/Linux.cpp b/clang/lib/Driver/ToolChains/Linux.cpp
index 59034bc..79deb04 100644
--- a/clang/lib/Driver/ToolChains/Linux.cpp
+++ b/clang/lib/Driver/ToolChains/Linux.cpp
@@ -1019,7 +1019,7 @@
 
   // Add linker option -u__llvm_runtime_variable to cause runtime
   // initialization module to be linked in.
-  if (!Args.hasArg(options::OPT_coverage))
+  if ((!Args.hasArg(options::OPT_coverage)) && (!Args.hasArg(options::OPT_ftest_coverage)))
     CmdArgs.push_back(Args.MakeArgString(
         Twine("-u", llvm::getInstrProfRuntimeHookVarName())));
   ToolChain::addProfileRTLibs(Args, CmdArgs);