Index: lib/Driver/ToolChains/Gnu.cpp
===================================================================
--- lib/Driver/ToolChains/Gnu.cpp
+++ lib/Driver/ToolChains/Gnu.cpp
@@ -85,6 +85,13 @@
           A->getOption().matches(options::OPT_W_Group))
         continue;
 
+      // Don't forward -mno-unaligned-access since GCC doesn't understand
+      // it and because it doesn't affect the assembly or link steps.
+      if ((isa<AssembleJobAction>(JA) || isa<LinkJobAction>(JA)) &&
+          (A->getOption().matches(options::OPT_munaligned_access) ||
+           A->getOption().matches(options::OPT_mno_unaligned_access)))
+        continue;
+
       A->render(Args, CmdArgs);
     }
   }
Index: test/Driver/gcc_forward.c
===================================================================
--- test/Driver/gcc_forward.c
+++ test/Driver/gcc_forward.c
@@ -34,3 +34,9 @@
 // RUN:   | FileCheck --check-prefix=CHECK-ASM %s
 // CHECK-ASM: as
 // CHECK-ASM-NOT: "-g"
+
+// Check that we're not forwarding -mno-unaligned-access.
+// RUN: %clang -target aarch64-none-elf -mno-unaligned-access %s -### 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-ARM %s
+// CHECK-ARM: gcc{{[^"]*}}"
+// CHECK-ARM-NOT: -mno-unaligned-access