[clang] Fix an unused variable warning

This patch fixes:

  clang/lib/Driver/ToolChains/PS4CPU.cpp:159:14: error: unused
  variable 'IsPS5' [-Werror,-Wunused-variable]

Author: kazutakahirata

clang/lib/Driver/ToolChains/PS4CPU.cpp

@@ -158,6 +158,7 @@ void tools::PScpu::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   const bool IsPS4 = TC.getTriple().isPS4();
   const bool IsPS5 = TC.getTriple().isPS5();
   assert(IsPS4 || IsPS5);
+  (void)IsPS5;
 
   ArgStringList DbgOpts;