Revert "Use dwarf exceptions on i686 as well"

This reverts commit ca43ab5ccd.

It was reported in https://github.com/mstorsjo/llvm-mingw/issues/8 that
the dwarf unwinding on i686 doesn't always work.

This commit adds a testcase for the case that didn't work previously.

wrappers/clang-target-wrapper.sh

@@ -10,8 +10,13 @@ esac
 ARCH=$(echo $TARGET | sed 's/-.*//')
 case $ARCH in
 i686)
-    # Dwarf is the default here.
-    ARCH_FLAGS=
+    # Dwarf is the default for i686, but libunwind sometimes fails to
+    # to unwind correctly on i686. This issue might be related to cases
+    # of DW_CFA_GNU_args_size (which were adjusted in libunwind SVN r337312).
+    # The issue can be reproduced with test/exception-locale.cpp.
+    # The issue goes away if building libunwind/libcxxabi/libcxx and the
+    # test example with -mstack-alignment=16 -mstackrealign.
+    ARCH_FLAGS=-fsjlj-exceptions
     ;;
 x86_64)
     # SEH is the default here.