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/Basic/Targets/PPC.h b/clang/lib/Basic/Targets/PPC.h
index 30f13c9..058970a 100644
--- a/clang/lib/Basic/Targets/PPC.h
+++ b/clang/lib/Basic/Targets/PPC.h
@@ -331,7 +331,7 @@
       break;
     }
 
-    if (getTriple().getOS() == llvm::Triple::FreeBSD) {
+    if (getTriple().isOSFreeBSD()) {
       LongDoubleWidth = LongDoubleAlign = 64;
       LongDoubleFormat = &llvm::APFloat::IEEEdouble();
     }