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.

run-tests.sh

@@ -16,7 +16,7 @@ TESTS_C="hello hello-tls crt-test setjmp"
 TESTS_C_DLL="autoimport-lib"
 TESTS_C_LINK_DLL="autoimport-main"
 TESTS_C_NO_BUILTIN="crt-test"
-TESTS_CPP="hello-cpp hello-exception tlstest-main"
+TESTS_CPP="hello-cpp hello-exception tlstest-main exception-locale"
 TESTS_CPP_DLL="tlstest-lib"
 TESTS_SSP="ssp"
 for arch in $ARCHS; do