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.

Dockerfile.dev

@@ -75,7 +75,7 @@ COPY test/*.cpp ./test/
 RUN cd test && \
     for arch in $TOOLCHAIN_ARCHS; do \
         mkdir -p $arch && \
-        for test in hello-cpp hello-exception tlstest-main; do \
+        for test in hello-cpp hello-exception tlstest-main exception-locale; do \
             $arch-w64-mingw32-clang++ $test.cpp -o $arch/$test.exe || exit 1; \
         done; \
         for test in tlstest-lib; do \