[Solaris] Only define _REENTRANT if -pthread

[ro]

Summary

When looking at lib/Basic/Targets/OSTargets.h, I noticed that _REENTRANT is defined
unconditionally on Solaris, unlike all other targets and what either Studio cc (only define
it with -mt) or gcc (only define it with -pthread) do.

This patch (on top of https://reviews.llvm.org/D41240) follows that lead.

[ro]

ping

[ro]

ping^2

[ro]

ping^3

[ro]

ping^4

[ro]

ping^5

[fedor.sergeev]

LGTM

lib/Basic/Targets/OSTargets.h

if (Opts.C99)
       Builder.defineMacro("_XOPEN_SOURCE", "600");
     else
       Builder.defineMacro("_XOPEN_SOURCE", "500");
     if (Opts.CPlusPlus)
       Builder.defineMacro("__C99FEATURES__");
     Builder.defineMacro("_LARGEFILE_SOURCE");
     Builder.defineMacro("_LARGEFILE64_SOURCE");
     Builder.defineMacro("__EXTENSIONS__");
+    if (Opts.POSIXThreads)
       Builder.defineMacro("_REENTRANT");
     if (this->HasFloat128)
       Builder.defineMacro("__FLOAT128__");
   }
 
 public:
   SolarisTargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : OSTargetInfo<Target>(Triple, Opts) {
     // FIXME: WIntType should be SignedLong