[asan] Add gcc 8's driver option -fsanitize=pointer-compare and -fsanitize=pointer-substract.

Disabled by default as this is still an experimental feature.

Reviewed By: thakis

Differential Revision: https://reviews.llvm.org/D59221

llvm-svn: 358285
diff --git a/clang/lib/Driver/ToolChains/FreeBSD.cpp b/clang/lib/Driver/ToolChains/FreeBSD.cpp
index 55586df..3a0bab8 100644
--- a/clang/lib/Driver/ToolChains/FreeBSD.cpp
+++ b/clang/lib/Driver/ToolChains/FreeBSD.cpp
@@ -410,6 +410,8 @@
   const bool IsMIPS64 = getTriple().isMIPS64();
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::Address;
+  Res |= SanitizerKind::PointerCompare;
+  Res |= SanitizerKind::PointerSubtract;
   Res |= SanitizerKind::Vptr;
   if (IsX86_64 || IsMIPS64) {
     Res |= SanitizerKind::Leak;