Replace getOS() == llvm::Triple::*BSD with isOS*BSD() [NFCI]

Replace multiple comparisons of getOS() value with FreeBSD, NetBSD,
OpenBSD and DragonFly with matching isOS*BSD() methods.  This should
improve the consistency of coding style without changing the behavior.
Direct getOS() comparisons were left whenever used in switch or switch-
like context.

Differential Revision: https://reviews.llvm.org/D55916

llvm-svn: 349752
diff --git a/clang/lib/Driver/XRayArgs.cpp b/clang/lib/Driver/XRayArgs.cpp
index 3d29499..1a48493 100644
--- a/clang/lib/Driver/XRayArgs.cpp
+++ b/clang/lib/Driver/XRayArgs.cpp
@@ -50,9 +50,9 @@
         D.Diag(diag::err_drv_clang_unsupported)
             << (std::string(XRayInstrumentOption) + " on " + Triple.str());
       }
-    } else if (Triple.getOS() == llvm::Triple::FreeBSD ||
-               Triple.getOS() == llvm::Triple::OpenBSD ||
-               Triple.getOS() == llvm::Triple::NetBSD ||
+    } else if (Triple.isOSFreeBSD() ||
+               Triple.isOSOpenBSD() ||
+               Triple.isOSNetBSD() ||
                Triple.getOS() == llvm::Triple::Darwin) {
       if (Triple.getArch() != llvm::Triple::x86_64) {
         D.Diag(diag::err_drv_clang_unsupported)