Fix driver warning about -shared-libasan on Android.

Asan runtime library is always shared on Android, and -shared-libasan is no-op.
Suppress the unused argument warning.

llvm-svn: 210252
diff --git a/clang/lib/Driver/SanitizerArgs.cpp b/clang/lib/Driver/SanitizerArgs.cpp
index c336195..0a74eed 100644
--- a/clang/lib/Driver/SanitizerArgs.cpp
+++ b/clang/lib/Driver/SanitizerArgs.cpp
@@ -171,8 +171,8 @@
 
   if (NeedsAsan) {
     AsanSharedRuntime =
-      (TC.getTriple().getEnvironment() == llvm::Triple::Android) ||
-      Args.hasArg(options::OPT_shared_libasan);
+        Args.hasArg(options::OPT_shared_libasan) ||
+        (TC.getTriple().getEnvironment() == llvm::Triple::Android);
     AsanZeroBaseShadow =
         (TC.getTriple().getEnvironment() == llvm::Triple::Android);
   }
diff --git a/clang/test/Driver/sanitizer-ld.c b/clang/test/Driver/sanitizer-ld.c
index cb29370..14b14b2 100644
--- a/clang/test/Driver/sanitizer-ld.c
+++ b/clang/test/Driver/sanitizer-ld.c
@@ -134,6 +134,14 @@
 // RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
 // RUN:     -target arm-linux-androideabi -fsanitize=address \
 // RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
+// RUN:     -shared-libasan \
+// RUN:   | FileCheck --check-prefix=CHECK-ASAN-ANDROID-SHARED-LIBASAN %s
+//
+// CHECK-ASAN-ANDROID-SHARED-LIBASAN-NOT: argument unused during compilation: '-shared-libasan'
+//
+// RUN: %clang -no-canonical-prefixes %s -### -o %t.o 2>&1 \
+// RUN:     -target arm-linux-androideabi -fsanitize=address \
+// RUN:     --sysroot=%S/Inputs/basic_android_tree/sysroot \
 // RUN:     -shared \
 // RUN:   | FileCheck --check-prefix=CHECK-ASAN-ANDROID-SHARED %s
 //