CppunitTest_xmlsecurity_signing Unit Test Failure on 32-bit Linux

[Luke Benes]

With both gcc and clang on Fedora 25, the build is failing with an assertion failure. This issue started with commit:

https://cgit.freedesktop.org/libreoffice/core/commit/?id=8242c22f84cef1bbc8c385875b2da4713b542329

[CUT] xmlsecurity_signing
SigningTest::testODFBrokenStreamGPG finished in: 639ms
SigningTest::testODFBrokenDsigGPG finished in: 5475ms
/core/unotest/source/cpp/macros_test.cxx:52:SigningTest::testODFEncryptedGPG
assertion failed
- Expression: xComponent.is()
- loading failed: file:///core//xmlsecurity/qa/unit/signing/data/encryptedGPG.odt

SigningTest::testODFEncryptedGPG finished in: 10168ms
macros_test.cxx:52:Assertion
Test name: SigningTest::testODFEncryptedGPG
assertion failed
- Expression: xComponent.is()
- loading failed: file:///core//xmlsecurity/qa/unit/signing/data/encryptedGPG.odt

Failures !!!
Run: 24   Failure total: 1   Failures: 1   Errors: 0

Error: a unit test failed, please do one of:

make CppunitTest_xmlsecurity_signing CPPUNITTRACE="gdb --args"
    # for interactive debugging on Linux

...

/core/solenv/gbuild/CppunitTest.mk:114: recipe for target '/core/workdir/CppunitTest/xmlsecurity_signing.test' failed
make[1]: *** [/core/workdir/CppunitTest/xmlsecurity_signing.test] Error 1
make[1]: *** Waiting for unfinished jobs....
Makefile:280: recipe for target 'build' failed
make: *** [build] Error 2


 $clang --version
clang version 7.0.0 (trunk 322869)
Target: i686-pc-linux-gnu
$ gcc --version
gcc (GCC) 6.4.1 20170727 (Red Hat 6.4.1-1)